fix: scope Claude review to PR diff only

The review prompt was too generic, causing Claude to review the entire
codebase instead of just the PR changes. Now explicitly instructs Claude
to use gh pr diff first and focus only on changed code.

Author: sbaerlocher

.github/workflows/ai-claude-review.yml

@@ -24,6 +24,10 @@ jobs:
         with:
           claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           prompt: |
-            Review this PR. Check code quality, bugs, performance, security.
-            Use CLAUDE.md for conventions. Post review via `gh pr comment`.
+            Review ONLY the changes in this PR, not the entire codebase.
+            First run `gh pr diff ${{ github.event.pull_request.number }}` to see the diff.
+            Then run `gh pr view ${{ github.event.pull_request.number }}` for context.
+            Focus your review on: code quality, bugs, performance, and security.
+            Use CLAUDE.md for project conventions if present.
+            Post your review as a single comment via `gh pr comment ${{ github.event.pull_request.number }}`.
           claude_args: '--allowed-tools "Bash(gh pr comment:*),Bash(gh pr diff:*),Bash(gh pr view:*)"'