Production-ready improvements: security hardening, Redis sessions, retry logic, updated pricing

Changes:
- Removed hardcoded admin credentials (now requires env vars)
- Added Redis session storage with in-memory fallback
- Improved CORS configuration with warnings for development mode
- Added retry_with_backoff decorator for translation API calls
- Updated pricing: Starter=, Pro=, Business=
- Stripe price IDs now loaded from environment variables
- Added redis to requirements.txt
- Updated .env.example with all new configuration options
- Created COMPREHENSIVE_REVIEW_AND_PLAN.md with deployment roadmap
- Frontend: Updated pricing page, new UI components

requirements.txt

@@ -25,3 +25,11 @@ PyJWT==2.8.0
 passlib[bcrypt]==1.7.4
 stripe==7.0.0
 
+# Session storage & caching (optional but recommended for production)
+redis==5.0.1
+
+# Database (optional but recommended for production)
+# sqlalchemy==2.0.25
+# asyncpg==0.29.0  # PostgreSQL async driver
+# alembic==1.13.1  # Database migrations
+