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/api/v1/usage.py

@@ -0,0 +1,17 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.ext.asyncio import AsyncSession
+from app.database import get_db
+from app.api.v1.deps import get_current_user_id
+from app.services.usage import UsageService
+
+router = APIRouter()
+
+
+@router.get("/stats")
+async def get_usage_stats(
+    user_id: str = Depends(get_current_user_id),
+    db: AsyncSession = Depends(get_db),
+):
+    svc = UsageService(db)
+    stats = await svc.get_usage_stats(user_id)
+    return stats