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

backend/env_template.txt

@@ -0,0 +1,8 @@
+# Clerk Authentication
+CLERK_SECRET_KEY=your_clerk_secret_key_here
+
+# Google Search Console
+GSC_REDIRECT_URI=http://localhost:8000/gsc/callback
+
+# Development Settings
+DISABLE_AUTH=false