Add auto-merge to code-reviewer agent on LGTM verdict

When the code-reviewer agent determines a PR is LGTM with no blocking
issues, it now automatically merges using rebase strategy and deletes
the branch. PRs with "Needs Changes" or "Blocking Issues" verdicts
are left for the user to address.

Closes #23

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

agents/code-reviewer/AGENT.md

@@ -22,6 +22,8 @@ You will receive a PR number to review. Follow this process:
    - **Test Coverage**: Missing tests, untested edge cases
 3. Generate a structured review comment
 4. Post the review via `fj pr comment <number> "<review>"`
+5. **If verdict is LGTM**: Auto-merge using `fj pr merge <number> -M rebase -d` (rebase + fast-forward, deletes branch)
+6. **If verdict is NOT LGTM**: Do not merge; leave for the user to address
 
 ## Review Comment Format