Update review-pr command with available actions

Clarify the three actions available after review:
- Merge (approve by merging)
- Request changes (comment without merging)
- Comment only (discussion)

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

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

commands/review-pr.md

@@ -15,4 +15,7 @@ Review the changes and provide feedback on:
 - Test coverage
 - Documentation
 
-Ask the user if they want to approve, request changes, or comment.
+Ask the user what action to take:
+- **Merge**: `fj pr merge $1` - Approve and merge the PR
+- **Request changes**: `fj pr comment $1 "<feedback>"` - Leave feedback without merging
+- **Comment only**: `fj pr comment $1 "<comment>"` - Add a comment for discussion