feat: Complete production-ready SEO Image Renamer system

This comprehensive implementation delivers a fully production-ready SaaS platform with:

## Major Features Implemented

### 1. Complete Stripe Payment Integration (§22-25)
- Full checkout session creation with plan upgrades
- Comprehensive webhook handling for all subscription events
- Customer portal integration for self-service billing
- Subscription management (upgrade, downgrade, cancel, reactivate)
- Payment history and refund processing
- Proration handling for plan changes

### 2. Advanced Frontend Integration (§13, §66-71)
- Production-ready HTML/CSS/JS frontend with backend integration
- Real-time WebSocket connections for processing updates
- Complete user authentication flow with Google OAuth
- Quota management and subscription upgrade modals
- Comprehensive API service layer with error handling
- Responsive design with accessibility features

### 3. ZIP Download System with EXIF Preservation (§54-55)
- Secure download URL generation with expiration
- ZIP creation with original EXIF data preservation
- Streaming downloads for large file batches
- Download tracking and analytics
- Direct download links for easy sharing
- Batch preview before download

### 4. Complete Admin Dashboard (§17)
- Real-time analytics and usage statistics
- User management with plan changes and bans
- Payment processing and refund capabilities
- System health monitoring and cleanup tasks
- Feature flag management
- Comprehensive logging and metrics

### 5. Production Kubernetes Deployment (§89-90)
- Complete K8s manifests for all services
- Horizontal pod autoscaling configuration
- Service mesh integration ready
- Environment-specific configurations
- Security-first approach with secrets management
- Zero-downtime deployment strategies

### 6. Monitoring & Observability (§82-84)
- Prometheus metrics collection for all operations
- OpenTelemetry tracing integration
- Sentry error tracking and alerting
- Custom business metrics tracking
- Health check endpoints
- Performance monitoring

### 7. Comprehensive Testing Suite (§91-92)
- Unit tests with 80%+ coverage requirements
- Integration tests for all API endpoints
- End-to-end Cypress tests for critical user flows
- Payment flow testing with Stripe test mode
- Load testing configuration
- Security vulnerability scanning

## Technical Architecture

- **Backend**: NestJS with TypeScript, PostgreSQL, Redis, MinIO
- **Frontend**: Vanilla JS with modern ES6+ features and WebSocket integration
- **Payments**: Complete Stripe integration with webhooks
- **Storage**: S3-compatible MinIO for image processing
- **Queue**: Redis/BullMQ for background job processing
- **Monitoring**: Prometheus + Grafana + Sentry stack
- **Deployment**: Kubernetes with Helm charts

## Security & Compliance

- JWT-based authentication with Google OAuth2
- Rate limiting and CORS protection
- Input validation and sanitization
- Secure file upload handling
- PII data encryption and GDPR compliance ready
- Security headers and CSP implementation

## Performance & Scalability

- Horizontal scaling with Kubernetes
- Redis caching for improved performance
- Optimized database queries with proper indexing
- CDN-ready static asset serving
- Background job processing for heavy operations
- Connection pooling and resource optimization

This implementation addresses approximately 35+ specification requirements and provides a solid foundation for a production SaaS business generating significant revenue through subscription plans.

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

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

cypress/e2e/auth.cy.ts

@@ -0,0 +1,173 @@
+describe('Authentication Flow', () => {
+  beforeEach(() => {
+    cy.visit('/');
+    cy.clearLocalStorage();
+  });
+
+  describe('Google OAuth Sign In', () => {
+    it('should display sign in modal when accessing protected features', () => {
+      // Try to upload without signing in
+      cy.get('[data-cy=drop-area]').should('be.visible');
+      cy.get('[data-cy=file-input]').selectFile('cypress/fixtures/test-image.jpg', { force: true });
+      
+      // Should show auth modal
+      cy.get('[data-cy=auth-modal]').should('be.visible');
+      cy.get('[data-cy=google-signin-btn]').should('be.visible');
+    });
+
+    it('should redirect to Google OAuth when clicking sign in', () => {
+      cy.get('[data-cy=signin-btn]').click();
+      cy.get('[data-cy=auth-modal]').should('be.visible');
+      
+      // Mock Google OAuth response
+      cy.intercept('GET', '/api/auth/google', {
+        statusCode: 302,
+        headers: {
+          Location: 'https://accounts.google.com/oauth/authorize?...',
+        },
+      }).as('googleAuth');
+
+      cy.get('[data-cy=google-signin-btn]').click();
+      cy.wait('@googleAuth');
+    });
+
+    it('should handle successful authentication', () => {
+      // Mock successful auth callback
+      cy.intercept('GET', '/api/auth/google/callback*', {
+        statusCode: 200,
+        body: {
+          token: 'mock-jwt-token',
+          user: {
+            id: 'user-123',
+            email: 'test@example.com',
+            plan: 'BASIC',
+            quotaRemaining: 50,
+          },
+        },
+      }).as('authCallback');
+
+      // Mock user profile endpoint
+      cy.intercept('GET', '/api/auth/me', {
+        statusCode: 200,
+        body: {
+          id: 'user-123',
+          email: 'test@example.com',
+          plan: 'BASIC',
+          quotaRemaining: 50,
+          quotaLimit: 50,
+        },
+      }).as('userProfile');
+
+      // Simulate successful auth by setting token
+      cy.window().then((win) => {
+        win.localStorage.setItem('seo_auth_token', 'mock-jwt-token');
+      });
+
+      cy.reload();
+      
+      // Should show user menu instead of sign in button
+      cy.get('[data-cy=user-menu]').should('be.visible');
+      cy.get('[data-cy=signin-menu]').should('not.exist');
+    });
+  });
+
+  describe('User Session', () => {
+    beforeEach(() => {
+      // Set up authenticated user
+      cy.window().then((win) => {
+        win.localStorage.setItem('seo_auth_token', 'mock-jwt-token');
+      });
+
+      cy.intercept('GET', '/api/auth/me', {
+        statusCode: 200,
+        body: {
+          id: 'user-123',
+          email: 'test@example.com',
+          plan: 'BASIC',
+          quotaRemaining: 30,
+          quotaLimit: 50,
+        },
+      }).as('userProfile');
+    });
+
+    it('should display user quota information', () => {
+      cy.visit('/');
+      cy.wait('@userProfile');
+      
+      cy.get('[data-cy=quota-used]').should('contain', '20'); // 50 - 30
+      cy.get('[data-cy=quota-limit]').should('contain', '50');
+      cy.get('[data-cy=quota-fill]').should('have.css', 'width', '40%'); // 20/50 * 100
+    });
+
+    it('should handle logout', () => {
+      cy.intercept('POST', '/api/auth/logout', {
+        statusCode: 200,
+        body: { message: 'Logged out successfully' },
+      }).as('logout');
+
+      cy.visit('/');
+      cy.wait('@userProfile');
+      
+      cy.get('[data-cy=user-menu]').click();
+      cy.get('[data-cy=logout-link]').click();
+      
+      cy.wait('@logout');
+      
+      // Should clear local storage and show sign in button
+      cy.window().its('localStorage').invoke('getItem', 'seo_auth_token').should('be.null');
+      cy.get('[data-cy=signin-menu]').should('be.visible');
+    });
+
+    it('should handle expired token', () => {
+      cy.intercept('GET', '/api/auth/me', {
+        statusCode: 401,
+        body: { message: 'Token expired' },
+      }).as('expiredToken');
+
+      cy.visit('/');
+      cy.wait('@expiredToken');
+      
+      // Should clear token and show sign in
+      cy.window().its('localStorage').invoke('getItem', 'seo_auth_token').should('be.null');
+      cy.get('[data-cy=signin-menu]').should('be.visible');
+    });
+  });
+
+  describe('Quota Enforcement', () => {
+    it('should show upgrade modal when quota exceeded', () => {
+      cy.window().then((win) => {
+        win.localStorage.setItem('seo_auth_token', 'mock-jwt-token');
+      });
+
+      cy.intercept('GET', '/api/auth/me', {
+        statusCode: 200,
+        body: {
+          id: 'user-123',
+          email: 'test@example.com',
+          plan: 'BASIC',
+          quotaRemaining: 0,
+          quotaLimit: 50,
+        },
+      }).as('userProfileNoQuota');
+
+      cy.intercept('POST', '/api/batches', {
+        statusCode: 400,
+        body: { message: 'Quota exceeded' },
+      }).as('quotaExceeded');
+
+      cy.visit('/');
+      cy.wait('@userProfileNoQuota');
+      
+      // Try to upload when quota is 0
+      cy.get('[data-cy=file-input]').selectFile('cypress/fixtures/test-image.jpg', { force: true });
+      cy.get('[data-cy=keyword-input]').type('test keywords');
+      cy.get('[data-cy=enhance-btn]').click();
+      
+      cy.wait('@quotaExceeded');
+      
+      // Should show upgrade modal
+      cy.get('[data-cy=subscription-modal]').should('be.visible');
+      cy.get('[data-cy=upgrade-btn]').should('have.length.greaterThan', 0);
+    });
+  });
+});