feat: ovens plugin framework + per-repo identity + review fixes

[apresmoi]

Turns ovens from a hardcoded special-case into a real framework, fixes the review
findings from #2/#3/#4, and adds CI + a publish workflow.

Ovens framework

• Handler registry: the server no longer imports the differential-testing
  engine or branches on id === "differential-testing". Each oven registers a
  handler (data, dashboard rows, background warm); unknown ids stay validated:false.
• Per-repo identity: custom ovens are identified by (repoKey, ovenId);
  built-ins are global. Discovery, /api/ovens, /api/ovens/:id?repoKey, oven-data,
  and run creation all resolve per repo — two repos with the same custom oven id
  never collide, and a run snapshots the correct repo's definition. oven bind,
  oven fork (writes oven.json lineage), per-repo binding stores.
• Atomic oven packages: custom ovens publish via a cross-platform pointer file
  (<id>/current -> rev-*), swapped by atomic file-rename. Reads are lock-free
  (resolve current once); GC is retirement-grace so a reader never hits ENOENT.
• Safety: oven writes require the target path be git-ignored (refused otherwise;
  burnlist init ignores .local/); paths are containedJoin-guarded against
  symlink escapes; malformed packages/bindings are isolated, never destroyed.
• Computed ovenRevision; run manifest schemaVersion 3 -> 4 (verified against snapshot).

Review fixes (#2 landing, #3 lifecycle, #4 ovens)

• Landing filter re-opens the matching project; duplicate-id rows route by plan path.
• Lifecycle moves are crash-safe (content-at-create lock, rename-then-digest with
  rollback, resumable/validated close).
• Per-row dashboard isolation: one bad oven/binding/plan never blanks the landing
  (it becomes a Blocked row). CLI oven list and /api/ovens isolate malformed packages.

CI/CD

• ci.yml: build + verify + package check on PRs and pushes to main, Node 18/20/22.
• publish.yml: manual dispatch (patch/minor/major); refuses non-main; commit-bound
  recovery — publishes/tags the exact npm artifact commit (gitHead), resumes from
  current origin/main, and fails on operational errors rather than mis-tagging.

The dashboard stays a read-only observer; only the CLI (and token-gated .local/
POSTs) mutate canonical state.

Note: publishing needs an NPM_TOKEN repo secret; the version bump happens in the
publish workflow.

[apresmoi]

Addressed the review — pushed 5 commits (63c0aa6..0877314).

Blockers

• Publish workflow: refuses non-main refs, pushes the bump+tag to main before npm publish, git push --atomic; CI now runs Node 18/20/22.
• Bindings resolved per-repo (no lexicographic shadowing): /api/oven-data/:id?repoKey= selects the repo's binding, falling back to the --oven-data override; DT dashboard rows are per bound repo.
• Lifecycle crash-safety: target reclaim via rmdirSync (empty-only — never deletes a real target); close is resumable (repairs a moved-but-digest-less burnlist) and re-validates + re-gates before repair; empty stale reservations are reclaimed.
• oven update now stages the package and swaps atomically (no more separate file writes).
• Generic handler returns validated:false for discovered custom ovens.

Completeness

• Added oven fork (writes the oven.json forkedFrom lineage, revision = source's ovenRevision).
• Removed the legacy definition.md/dashboard.json/types/ fallbacks from the CLI (matches the server).

Deferred (documented): oven update is not yet a fully atomic read snapshot — a reader doing two sequential reads can still straddle the dir swap. The correct fix (immutable revision dirs behind a resolved-once pointer) is folded into the upcoming .oven/layout.json packaging work rather than duplicated here.

Scope unchanged: this is the framework slice; the .oven DSL, component library, and renderer deletion are the next PR. npm run verify green (229 tests), build + package + global-install pass, zero runtime deps, files <400 lines.