feat: Complete Google Search Console integration with Clerk authentication

- Add GSC API service with OAuth2 authentication
- Implement Clerk authentication for frontend and backend
- Add GSC login button and OAuth callback handling
- Create comprehensive GSC data fetching and caching
- Add authentication middleware for backend API protection
- Implement real-time GSC data integration in SEO dashboard
- Add user-specific GSC site management
- Include comprehensive logging and error handling
- Add TypeScript support and proper type definitions
- Create environment templates and setup documentation
- Update gitignore to exclude sensitive credential files

Features added:
- GSC OAuth2 authentication flow
- Real-time search analytics data
- Site list management
- Sitemap analysis
- User-specific data isolation
- Comprehensive error handling
- Authentication token management
- Popup-based OAuth flow
- Data caching and refresh mechanisms

Note: gsc_credentials.json should be created locally with your Google OAuth credentials

.gitignore

@@ -35,6 +35,10 @@ backend/content_cache.db
 backend/outline_cache.db
 backend/research_cache.db
 
+# Google OAuth credentials
+gsc_credentials.json
+**/gsc_credentials.json
+
 # Onboarding progress files
 .onboarding_progress.json
 backend/.onboarding_progress.json