Add METANET (Plesk) provider support

[rtanglao]

Add METANET (Plesk) provider support

Add metanet-plesk as a remediation provider in records.json so both the CLI
(--provider metanet-plesk) and the web app emit METANET-Plesk-specific fix instructions
for the 13-record Thundermail set (1 MX, 5 SRV, 4 TXT, 3 DKIM CNAME).

Internal ticket: TBPRO 7194
(7194_METANET_PLESK).

METANET (metanet.ch, Swiss host) exposes DNS through the Plesk Administration Tool
("DNS-Einstellungen" → Ressourceneintrag zur Zone hinzufügen), in a German-language UI.
This is the first Plesk-based panel we support, and it is the most field-granular one so
far — the SRV form has seven inputs.

⚠️ Ship as UNVERIFIED first, per the godaddy/ionos/ovh/hover/digitalocean/porkbun
precedent: prefix each header string UNVERIFIED — until confirmed end-to-end, then drop
the prefix. The SRV field layout below is confirmed from a screenshot of the live
Ressourceneintrag bearbeiten form on thundermail.example.org; the TXT form is
confirmed from METANET's own docs; MX and CNAME field labels are not yet confirmed
(standard-Plesk guesses — see Open questions).

🎯 thundermail.example.org is the verification target. It is a METANET Plesk zone
delegated to ns1.hera.metanet.ch / ns2.hera.metanet.ch, so query it authoritatively:
uv run verify_thundermail_dns.py thundermail.example.org --resolver ns1.hera.metanet.ch
Live web preview: https://thunderbird.github.io/dns-scripts/?domain=thundermail.example.org
Current state: 8 passed, 5 failed — MX, all 4 TXT and all 3 DKIM CNAMEs are correct;
all 5 SRV records fail. See the blocker below.

🚨 Blocker: SRV weight 1 cannot be entered in Plesk

Plesk renders the SRV weight ("Relative Gewichtung für Einträge mit gleicher
Priorität") as a dropdown with fixed steps of 5, not a free-text field. The options are:

sehr hoch (50), 45, 40, 35, 30, 25, 20, 15, 10, 5, niedrig (0)

Our record set specifies weight: 1 for all five SRV records, and value_templates.SRV
uses match_mode: "exact" — so a METANET/Plesk user literally cannot make the checker
pass. This is confirmed live: the operator picked niedrig (0), and all five SRV records
now read 0 0 <port> mail.thundermail.com against an expected 0 1 <port> …:

FAIL _jmap._tcp        expected: 0 1 443 mail.thundermail.com
                            got: 0 0 443 mail.thundermail.com
FAIL _caldavs._tcp     expected: 0 1 443 mail.thundermail.com
                            got: 0 0 443 mail.thundermail.com
FAIL _carddavs._tcp    expected: 0 1 443 mail.thundermail.com
                            got: 0 0 443 mail.thundermail.com
FAIL _imaps._tcp       expected: 0 1 993 mail.thundermail.com
                            got: 0 0 993 thundermail.example.org   <- also a wrong target
FAIL _submission._tcp  expected: 0 1 587 mail.thundermail.com
                            got: 0 0 587 mail.thundermail.com

(The _imaps target is separately wrong — the Zielhost field ended up holding the zone apex
instead of mail.thundermail.com; the operator can fix that one. The weight mismatch on all
five is the structural problem.)

This needs a decision before the provider block is finalized, because whatever we emit
for the Weight field is either unselectable or knowingly non-matching:

• Option A (recommended): stop comparing SRV weight. With a single target in the RRset
  the weight has no operational effect — relative weighting only matters between multiple
  targets at the same priority. Add a match mode (e.g. exact_ignore_weight) to
  value_templates.SRV, implemented in both interpreters + a parity fixture + linter case.
  This unblocks METANET/Plesk and any other panel with a constrained weight picker, and
  costs nothing in correctness.
• Option B: change the canonical weight to 0 in records.json (Thundermail-side call —
  needs sign-off from whoever owns the published Thundermail setup instructions, and would
  flag every domain that currently has weight 1).
• Option C: emit niedrig (0) and accept a permanent FAIL for METANET users. Rejected —
  it breaks the "exit 0 ⟺ everything correct" contract.

Option A is probably its own small issue that this one depends on; note the interaction
before writing the metanet-plesk block.

Add-record model

Plesk uses one add-record form with an Eintragstyp (entry type) dropdown — like
bunny/godaddy/hover/digitalocean/porkbun, not per-type sections like
cosmotown. Offered types: NS, A, AAAA, CNAME, MX, PTR, TXT, SRV, DS, CAA.

Path: Plesk → Websites & Domains → your domain → DNS-Einstellungen → Eintrag hinzufügen
→ pick Eintragstyp, fill the fields, Übernehmen (Apply) — then click Aktualisieren
(Update) on the yellow banner to commit.

Key conventions:

• Apex host = BLANK. The Domainname field is left empty; the panel prints the zone
  suffix (.thundermail.example.org.) immediately to the right of the input. So this is the
  blank-apex pattern of bunny/cosmotown/ovh/porkbun — use {subhost} for
  MX/TXT/CNAME (never @), and {srvsubhost} for the SRV Domainname (blank at the
  apex, the token that exists for hover).
• SRV splits Service and Protocol into separate fields — WITHOUT the leading underscore.
  Both fields carry the hint "Beispiel: SIP (ohne Unterstrich)" ("Example: SIP, without
  underscore"), and the live screenshot shows imaps / tcp typed bare. Our existing
  {service} / {protocol} tokens yield _imaps / _tcp with the underscore
  (godaddy/ionos/hover want them that way), so METANET needs two new interpreter tokens
  — see below. This is the first provider that strips the underscore.
• Priority and Weight are dropdowns, not text inputs. Priorität shows
  sehr hoch (0) for 0 (0 is selectable, so SRV priority is fine; MX priority 10 is in the
  list too — METANET's own default template ships MX 10 mail.<domain>.). Relative Gewichtung is the constrained one — see the blocker above.
• Weight, Port and Target are three separate fields (Relative Gewichtung, Zielport,
  Zielhost) — so SRV uses the individual {weight} / {port} / {target} tokens like
  namecheap/hover, not the packed {value}.
• Targets are stored verbatim — NO trailing dot needed. Confirmed live: four of the five
  SRV records hold exactly mail.thundermail.com. and the MX holds 10 mail.thundermail.com., i.e. Plesk appends the root dot itself and does not append the
  zone name. So emit plain {target} like bunny/porkbun, not {target}. like
  ovh/digitalocean.
• TXT values are auto-quoted by the panel. METANET's docs are explicit: "The entry type
  TXT automatically sets the including quotation marks (example: "MS=ms14335100"). In this
  example, you would therefore only enter MS=ms14335100." So emit the unquoted {value} —
  same as cosmotown. Field label is TXT-Eintrag.
• Two-step save. New/changed entries are marked with an exclamation mark and are not
  live until Aktualisieren is clicked on the pending-changes banner; several edits can be
  batched. Worth calling out in the headers so users don't add all 13 records and conclude
  the tool is broken. Propagation can then take several hours.

New interpreter tokens

Add to the resolve_record / resolveRecord SRV-label split, in both Python and JS
(the sync rule), plus a tests/fixtures/parity_cases.json case:

Token	Value for _imaps._tcp	Why
{bareservice}	imaps	{service} minus the leading _ — Plesk's Service-Name
{bareprotocol}	tcp	{protocol} minus the leading _ — Plesk's Protokoll

(Name bikeshed welcome — {bareservice}/{bareprotocol} reads consistently with the
existing {service}/{protocol}/{srvhost}/{srvsubhost} family.) Computed for all
records like the rest of the split tokens, referenced only by the metanet-plesk SRV
template. Remember: the records.json linter asserts every template interpolates with no
unknown/leftover token, so the tokens must land before the provider block.

Field mapping

Type	Fields (Plesk label → value)
MX	Eintragstyp=MX, Domainname={subhost} (blank at apex), Mail-Exchange-Server={target}, Priorität={priority} (dropdown)
SRV	Eintragstyp=SRV, Service-Name={bareservice} (imaps, no underscore), Protokoll={bareprotocol} (tcp, no underscore), Domainname={srvsubhost} (blank at apex), Priorität={priority} (dropdown, sehr hoch (0)), Relative Gewichtung=see blocker, Zielhost={target}, Zielport={port}
TXT	Eintragstyp=TXT, Domainname={subhost} (blank at apex), TXT-Eintrag={value} (no quotes — the panel adds them)
CNAME	Eintragstyp=CNAME, Domainname={subhost} (DKIM label), Kanonischer Name={target}

SPF / MTA-STS / TLSRPT / DMARC are all plain TXT; DKIM here is a CNAME.
Service-Name, Protokoll and Zielport are the SRV form's required (*) fields.

Work items

• Resolve the SRV weight blocker (Option A recommended — a match_mode that ignores
  SRV weight, in records.json + both interpreters + tests). Possibly a separate issue
  this one depends on.
• Add {bareservice} / {bareprotocol} to the SRV-label split in
  verify_thundermail_dns.py and app.js, plus a parity_cases.json fixture.
• Add the metanet-plesk provider block to records.json (headers UNVERIFIED —
  prefixed): {subhost} apex, {srvsubhost} SRV apex, bare service/protocol, separate
  Weight/Port/Target, plain {target} (no trailing dot), unquoted TXT.
• Decide the label language — German labels as shown in the panel, or German with an
  English gloss (see Open questions).
• Mention the Aktualisieren (Update) commit step in the headers.
• uv run verify_thundermail_dns.py example.com --provider metanet-plesk renders all 13
  records in both --fix-format table and long without error.
• Web app "metanet-plesk" provider mirrors the CLI output (table + detailed).
• uv run python -m unittest discover -s tests -t . -v green (linter + parity).
• Update README.md provider list + RELEASE_NOTES.md and RELEASE_NOTES.html.
• Update CLAUDE.md crucial-decisions with METANET/Plesk's quirks (blank apex,
  underscore-less Service/Protocol, dropdown Priority/Weight, verbatim targets,
  auto-quoted TXT, two-step save, German UI).
• Verify against thundermail.example.org (--resolver ns1.hera.metanet.ch): confirm
  the MX and CNAME field labels on the live panel, fix the _imaps Zielhost, then drop
  the UNVERIFIED — prefixes.

Open questions

• Provider key / label. metanet-plesk (as in the ticket) vs plain plesk — the form
  layout is stock Plesk and would serve any Plesk host, but the verbatim-target and
  auto-quoting behaviours were only confirmed on METANET's build. Recommendation: ship
  metanet-plesk now; generalise to plesk only if another Plesk host shows up.
• Label language. Every existing provider uses the panel's own English labels. METANET's
  Plesk is German (Plesk can switch UI language). Emit the German labels verbatim
  (Zielhost), or German + gloss (Zielhost (Target host))? Recommendation: German
  verbatim, since that's what the user sees, with the English hint in the header text.
• MX / CNAME field labels are unconfirmed. Mail-Exchange-Server and Kanonischer Name
  above are standard-Plesk German labels, not read off a live METANET form — the docs only
  screenshot the NS, TXT and SRV forms. Grab MX and CNAME add-record screenshots before
  dropping UNVERIFIED.
• Subdomain zone. thundermail.example.org is a delegated subdomain zone (its own
  Plesk DNS zone, apex = thundermail.example.org). Nothing special for us — the tool just
  takes that as the domain — but note it when reading the screenshot's .thundermail.example.org.
  suffix.
• Escape hatch. METANET sells a Premium Service: Individual DNS settings — email
  support@metanet.ch with the records in copyable form and they enter them. Worth a line in
  the headers (or an SRV-specific fallback, as cosmotown routes SRV to support) if the
  weight blocker isn't resolvable.

Reference docs

• Plesk: DNS-Verwaltung (German, official) — https://www.metanet.ch/de/support/dns-nameserver/dns/plesk-dns-verwaltung
• Local PDFs: THUNDERBIRD_2023/TBPRO/7194_METANET_PLESK/Plesk_ DNS-Verwaltung.pdf (German)
  and translated-to-english-by-firefoxl-pesk_ DNS-Verwaltung.pdf (Firefox translation).
• Live SRV form screenshot (with the Weight dropdown open, showing the 0/5/10…50 steps):
  THUNDERBIRD_2023/TBPRO/7194_METANET_PLESK/SRV Einträge 2.jpg

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