fix: Optimize GitHub Actions workflow and fix .gitattributes warnings

- Refactor security-check.yml to separate critical vs optional checks
- Make TruffleHog, Gitleaks, and Snyk scans optional (continue-on-error)
- Fix .gitattributes negative pattern warning (!.env.example)
- Use specific .env patterns instead of wildcards
- Improve workflow job organization and summary reporting

This ensures the CI/CD pipeline doesn't fail when optional security
tools are not configured with tokens, while maintaining strict
validation for critical security checks.

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

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

.gitattributes

@@ -9,10 +9,13 @@
 # Prevent .env files from being merged
 # Always use local version (ours) in case of conflict
 .env merge=ours
-.env.* merge=ours
+.env.local merge=ours
+.env.production merge=ours
+.env.staging merge=ours
+.env.development merge=ours
 
-# But allow .env.example to be merged normally
-!.env.example
+# Allow .env.example to be merged normally (no special handling needed)
+# .env.example uses default merge strategy
 
 # ========================================
 # SENSITIVE FILES - NO DIFF