fix(hook,mcp): no-op hook outside zg repos + clear draft pin on tick

[morrieinmaas]

Summary

Three real-use bugs surfaced by a user on sensor-sender:

1. Pre-commit hook blocks every commit in non-zg repos. A stale install (or a partial init) left a hook that ran zettelgeist regen --check, which hard-errors with not a zettelgeist repo whenever .zettelgeist.yaml is missing. Fix: the installed hook block now exits 0 silently when the config file is missing. Existing broken installs heal on the next zettelgeist install-hook / zettelgeist init run.

2. Spec stuck in draft after all tasks ticked (write-side prevention). The board's "+" button pins status: draft in frontmatter so the new card lands in the draft column. Nothing ever cleared the pin, so the frontmatter override beat the derived status forever. Fix: tick_task strips a status: draft override on requirements.md as part of the same commit (other override values left alone; untick_task does not clear, so reset-to-draft still works).

3. Existing stuck specs self-heal on next render (read-side rescue). The write-side fix only helps if the user ticks ANOTHER task — useless for the spec already in the bug state (every task ticked, override pinned). Fix: deriveStatus now ignores a status: draft override when at least one counted task exists and every counted task is checked. No file mutation, no migration, no user action — stuck specs unstick on next viewer/extension load.

Changes

• packages/git-hook/src/install-hook.ts — add [ -f .zettelgeist.yaml ] || exit 0 to HOOK_BLOCK.
• packages/mcp-server/src/tools/write.ts — tickOrUntick strips a status: draft override on tick via a multi-file atomic write.
• packages/mcp-server/src/util/write-and-commit.ts — new extraWrites?: ReadonlyArray<{ relPath, content }> option. Helper writes all files via temp+rename before running conformance, so a conformance throw leaves a consistent working-tree diff rather than a torn state (failure mode symmetric with the existing single-file case).
• packages/core/src/status.ts — deriveStatus ignores status: draft override when all counted tasks are checked.
• Tests added across all three layers (incl. negative: other overrides untouched, untick does not clear, partial-progress draft pin honored, conformance fixture 19-all-statuses/a-draft unaffected because counted.length === 0).
• Three changesets (core patch, cli patch, mcp-server patch). git-hook is in ignore so its change ships via the cli's install-hook command.

Code review

Independent code-reviewer agent flagged one real issue: the original write-side patch wrote requirements.md to disk before writeFileAndCommit ran conformance — an asymmetric write pattern with a half-applied failure mode. Addressed in commit 4dadf60 (atomic multi-file write via extraWrites). Also added a test for the status-only-frontmatter edge case that the reviewer noted was uncovered.

Reviewer-noted concerns acknowledged but not changed:

• Read-side self-heal could surprise a user who pinned draft on a single-task spec deliberately — narrow enough we accept it; the alternative is users with stuck cards.
• Hook block test brittleness on PATH — accepted as-is.

Test plan

• pnpm -r typecheck — clean
• pnpm -r test — all 9 packages, all green (190 core / 45 mcp / 117 cli / +others)
• pnpm conformance — 46 fixtures pass
• After merge: confirm Changesets bot opens "Version Packages" PR with core + cli + mcp-server patch bumps
• After version PR merges: rebuild VSCode extension with new git-hook block + new core and ship the vsix