Hook auto-update: warn when rtk-rewrite.sh is outdated #344

Problem

Users who installed the hook before v0.25.0 (PR #241) still have the old 200+ line bash hook that:

• Duplicates all rewrite logic (instead of delegating to rtk rewrite)
• Ignores [hooks] exclude_commands config (Support exclude_commands config for auto-rewrite hook #243/fix: curl JSON size guard (#297) + exclude_commands config (#243) #342)
• Won't benefit from any future rewrite rule changes without manual rtk init -g

There's no mechanism to detect or update stale hooks. Users stay on the old version silently.

Proposal

Add a hook version check on rtk startup:

1. Add a version comment at the top of the hook: # rtk-hook-version: 2
2. On startup (or on rtk rewrite), check the installed hook file
3. If the hook is outdated (missing version tag or old version), print a one-line warning to stderr:

   [rtk] Hook outdated — run `rtk init -g` to update
   

4. Show the warning at most once per day (marker file, same pattern as telemetry)

Why not auto-patch?

The hook file lives in user space (~/.claude/hooks/). Silently modifying it could break custom modifications. A warning is safer and lets the user decide when to update.

Acceptance criteria

• Hook file has a # rtk-hook-version: N header
• rtk rewrite checks installed hook version
• Warning printed to stderr if outdated (max 1/day)
• rtk init -g bumps the version header
• rtk init --show displays hook version status