Use GitHub-hosted runner for PR automation

Self-hosted runner requires per-repo registration.
GitHub-hosted runner works out of the box with ANTHROPIC_API_KEY secret.

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

Author: GiggleLiu

.github/workflows/pr-automation.yml

@@ -15,7 +15,7 @@ jobs:
 
     # Use self-hosted runner to run Claude on your local machine
     # Change to 'ubuntu-latest' to run on GitHub-hosted runners instead
-    runs-on: self-hosted
+    runs-on: ubuntu-latest
 
     permissions:
       contents: write