Address the non-red-team documentation/cleanup items from review #1679:
- Document the GIT_SYNC_BACKEND_TIMEOUT_MS watchdog (git http-backend) in
.env.example and add it to the environment validation schema — it was used
(getGitSyncBackendTimeoutMs, default 120000) but undocumented/unvalidated.
- Remove the dead GIT_SYNC_DEBOUNCE_MS_DEFAULT / GIT_SYNC_POLL_INTERVAL_MS_DEFAULT
exports (never imported; environment.service is the single source of defaults).
- Redirect the dangling `plan §X.Y` comment references to issue #194 (the
git-sync spec moved there when docs/git-sync-plan.md was deleted by this PR).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>