Add optional git-hook triggers for sync

[ivklgn]

Problem

Sync must be run manually; there's no way to trigger it automatically on git activity.

Expected result

Optional, opt-in git-hook triggers (e.g. post-commit / post-merge) that run a push sync — easy to install and remove, mirroring the existing hooks patterns.

Impact

Keeps the server in sync with the repo without the user remembering to run sync.

Scope

• Add opt-in install of a git hook that runs sync.
• Make it safe/idempotent and cleanly removable.
• Guard against excessive triggering.
• Tests for install/remove.

Files: a sync hook installer alongside the existing cmd/hooks* patterns (+ tests)

Acceptance: users can opt into automatic sync on git events and cleanly remove it.

Status: blocked — the sync feature is currently gated off at the command layer.