Only trigger Claude Code review on PR open, not every push

For re-reviews after subsequent pushes, authors can comment
"@claude review" which triggers via the assist flow.

Co-authored-by: Isaac

Author: shreyas-goenka

.github/workflows/claude-code.yml

@@ -9,7 +9,7 @@ name: Claude Code
 
 on:
   pull_request:
-    types: [opened, synchronize, reopened]
+    types: [opened]
 
   issue_comment:
     types: [created]
@@ -18,7 +18,7 @@ on:
     types: [created]
 
 jobs:
-  # Automatic PR review when a PR is opened or updated.
+  # Automatic review on PR open. For re-reviews, comment "@claude review".
   review:
     if: github.event_name == 'pull_request'
     concurrency: