fix VerseRef.verseNum setter mis-port

[irahopkinson]

The verseNum setter assigned the backing field and nothing else, still carrying
its ToDo placeholder:

set verseNum(value: number) {
  // ToDo: replace or remove this placeholder
  this._verseNum = value;
}

The C# VerseRef.VerseNum
it ports does two more things:

set
{
    if (value < 0)
        throw new VerseRefException("VerseNum can not be negative");
    verseNum = (short)value;
    verse = null;          // <- clears the range/segment string
}

So the TS accepted negative verse numbers, and assigning verseNum left any
range or segment string in place:

const vref = new VerseRef('LUK', '3', '4b-5a');
vref.verseNum = 9;
vref.verse;        // '4b-5a' (stale) — now '9'
vref.hasMultiple;  // true (stale)    — now false

This mirrors #58, which fixed the sibling chapterNum setter the same way.
this._verse = undefined is used rather than null, per the repo convention of
preferring undefined for missing values, and the C# (short) cast is not
replicated.

⚠️ This one is a consumer-visible behaviour change

Unlike chapterNum — which recursed into itself and blew the stack on every
assignment, so nothing could have depended on it — this setter works today.
Clearing _verse changes what the verse getter and hasMultiple return for
code that currently functions: anything that assigns verseNum to a ref holding
a range or segment and then reads verse will now get the new number instead of
the old range string.

That is the correct, C#-faithful behaviour, and the old value was stale/incorrect
— but it is a break, not a pure bugfix in the semver sense. This may warrant
more than a patch bump. No version bump is included here; that call is left to
the maintainer.

Tests

Worked TDD: tests written first, confirmed red (3 failures — no throw on
negative, '4b-5a' and '4b' both stale), then fixed.

The C# test that actually covers the range-clearing is CopyVerseFrom — it sets
VerseNum = 9 on a LUK 3:4b-6a source, then asserts the copied Verse is
"9" rather than "4b-6a". It can't be ported yet: copyVerseFrom isn't
implemented in this port. Nothing else in VerseRefTests.cs assigns VerseNum
on a ranged ref, so the cases go in the existing
describe('Extra (TS-only tests)') > describe('Property setters') block
alongside the chapterNum ones:

• negative throws VerseRefException
• zero is allowed (boundary guard)
• assigning verseNum clears a range ('4b-5a' → '9', hasMultiple false)
• assigning verseNum clears a segment ('4b' → '9')

BuildVerseRefByProps already exercised verseNum = 0/15/17 and still passes —
those are plain numbers with no verse string to clear.

Also removes the now-fixed set verseNum bullet from CLAUDE.md's "Known porting
gaps".

Verification

Full CI sequence, all passing:

npm run lint && npm run prettier:ci && npm run build && npx vitest run

• lint — clean at --max-warnings 0
• prettier:ci — no files differ
• build — tsc clean, dist/ regenerated with no unexpected diff
• vitest run — 47 passed (3 files)
• npx tsc -p tsconfig.test.json --noEmit — clean (CI doesn't run this; test
  files are otherwise unchecked)

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.68%. Comparing base (32d457b) to head (03101cb).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #60      +/-   ##
==========================================
+ Coverage   83.93%   84.68%   +0.74%     
==========================================
  Files           4        4              
  Lines         330      333       +3     
  Branches       77       80       +3     
==========================================
+ Hits          277      282       +5     
+ Misses         33       30       -3     
- Partials       20       21       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.