Fix PR automation permissions by using pull_request_target event

- Changed from pull_request to pull_request_target to fix fork permissions
- Added explicit PR head SHA checkout for proper code validation
- Resolves 'Resource not accessible by integration' errors
- Enables label adding and comment posting from forked PRs

This allows automation to work correctly for external contributors.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: Karanjot786

.github/workflows/pr-automation.yml

@@ -1,7 +1,7 @@
 name: 🤖 PR Automation
 
 on:
-  pull_request:
+  pull_request_target:
     types: [opened, synchronize, reopened]
     branches: [main]
 
@@ -23,6 +23,7 @@ jobs:
     - name: 📥 Checkout code
       uses: actions/checkout@v4
       with:
+        ref: ${{ github.event.pull_request.head.sha }}
         fetch-depth: 0
 
     - name: 🔍 Get changed files