Add landing page, referral system, usage quotas, search API management, and yearly pricing

- Separate workspace landing from login for better UX
- Referral system rewards both parties with Pro days
- Quota enforcement prevents abuse without breaking endpoints
- 7-day free trial with auto-downgrade on expiry
- Admin-managed search provider config (SearXNG, Bing)
- 15% discount on annual subscriptions
- MCP search server wrapping opencode search
- Fix discovery module field name mismatch causing 422

backend/app/config.py

@@ -100,6 +100,8 @@ class Settings(BaseSettings):
     FREE_MAX_PRODUCTS: int = 1
     FREE_DAILY_QUOTATIONS: int = 3
 
+    TRIAL_DAYS: int = 7
+
     PRO_DAILY_TRANSLATE_CHARS: int = 50000
     PRO_DAILY_REPLIES: int = 200
     PRO_DAILY_MARKETING: int = 50