ci: stop auto-running Claude PR review on every pull request

Removes the pull_request trigger so the workflow only runs on explicit
@claude mentions or manual workflow_dispatch.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/claude-review.yml

@@ -1,8 +1,6 @@
 name: Claude PR Review
 
 on:
-  pull_request:
-    types: [opened, synchronize]
   issue_comment:
     types: [created]
   pull_request_review_comment:
@@ -24,7 +22,6 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 30
     if: |
-      github.event_name == 'pull_request' ||
       github.event_name == 'workflow_dispatch' ||
       (github.event_name == 'issue_comment' &&
        github.event.issue.pull_request &&