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/models/referral.py

@@ -0,0 +1,26 @@
+from sqlalchemy import Column, String, Integer, DateTime, ForeignKey, Boolean
+from sqlalchemy.dialects.postgresql import UUID
+from datetime import datetime
+from app.database import Base
+import uuid
+
+
+class ReferralCode(Base):
+    __tablename__ = "referral_codes"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    user_id = Column(UUID(as_uuid=True), nullable=False, index=True)
+    code = Column(String(20), unique=True, nullable=False, index=True)
+    created_at = Column(DateTime, default=datetime.utcnow)
+
+
+class Referral(Base):
+    __tablename__ = "referrals"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    referrer_id = Column(UUID(as_uuid=True), nullable=False, index=True)
+    referred_id = Column(UUID(as_uuid=True), nullable=False, unique=True)
+    code = Column(String(20), nullable=False)
+    reward_days = Column(Integer, default=15)
+    status = Column(String(20), default="completed")
+    created_at = Column(DateTime, default=datetime.utcnow)