Skip Trivy security scan for pull requests

Security scanning requires pushed images, which are not available
in PR context. Only run security scans on push events.

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

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

.github/workflows/deploy.yml

@@ -103,6 +103,7 @@ jobs:
     name: Security Scanning
     runs-on: ubuntu-latest
     needs: build
+    if: github.event_name != 'pull_request'
     
     steps:
       - uses: actions/checkout@v4