fix(app): refresh review panel on external git commits

[lxqddd]

Issue for this PR

Closes #40795
Relates to #11856

Type of change

• Bug fix

What does this PR do?

The review panel caches its vcs.diff query with every refetch hook disabled (refetchOnWindowFocus/Mount/Reconnect: false), so it only refreshes through explicit invalidation. Most terminal git operations still refresh it by accident — pull/checkout/merge rewrite workspace files and produce non-.git watcher events, and switching tabs or the review mode re-triggers the query.

But an out-of-band git commit / git add / git commit --amend rewrites only files under .git, and none of that produced an event, so the panel kept showing the pre-commit changes until some unrelated event happened to refresh it (a file edit, a session finishing, reopening the panel):

• Server-side, the .git subscription watches only HEAD, and a regular commit doesn't change HEAD's content — it's still the same symbolic ref
• Client-side, the session VCS listener dropped every .git path anyway (that check also compared a relative .git/... prefix against absolute event paths, so it never actually matched)
• The branch name (part of the query key) doesn't change either, so the query never re-ran

Fix:

• core watcher: also exempt index from the .git ignore list — staging and commits rewrite it; the rest of .git stays ignored so we don't flood events
• app session: treat paths under .git whose basename is index or HEAD as VCS state changes and call the existing debounced refreshVcs(); basename matching also covers git worktrees (.git/worktrees/<name>/index)
• test: flip ignores .git/index changes to assert the event is published, and add coverage that other .git files (COMMIT_EDITMSG) remain ignored

How did you verify your code works?

• bun test test/filesystem/watcher.test.ts — 7/7 pass, including the new publishes .git/index events and ignores other .git changes tests
• typecheck passes for packages/core and packages/app
• Manually in the desktop app: review panel open, git commit / git add from a terminal → panel refreshes within the 100ms debounce; unrelated .git churn stays silent

Screenshots / recordings

No visual UI change — behavior fix only.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR