fix: add pull-requests write permission to release workflow

The reusable release workflow declares pull-requests:write but the
caller didn't grant it, causing startup_failure on GitHub Actions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/release.yaml

@@ -10,6 +10,7 @@ on:
 
 permissions:
   contents: write
+  pull-requests: write
 
 jobs:
   release: