Add car_id column to RequestVehicle model

- Add car_id foreign key to link recommended vehicles to cars table
- Add car relationship for easier access

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/models/vehicle_request.py

@@ -49,7 +49,10 @@ class RequestVehicle(Base):
     id = Column(Integer, primary_key=True, index=True)
     request_id = Column(Integer, ForeignKey("vehicle_requests.id"), nullable=False)
 
-    # Car data from Carmodoo (stored as JSON)
+    # Reference to imported car in cars table
+    car_id = Column(Integer, ForeignKey("cars.id"), nullable=True)
+
+    # Car data from Carmodoo (stored as JSON for backup/display)
     car_data = Column(JSON, nullable=False)
 
     # Admin approval
@@ -60,6 +63,7 @@ class RequestVehicle(Base):
 
     # Relationships
     request = relationship("VehicleRequest", back_populates="recommended_vehicles")
+    car = relationship("Car", backref="request_vehicles")
 
 
 class PurchasedVehicle(Base):