fix: remove legacy TCO fields from vehicle forms (refs #37)

- Remove CostInterval type and TCOResponse interface from frontend types
- Remove insurance/registration cost fields from VehicleForm schema and UI
- Keep purchasePrice and purchaseDate fields on vehicle form
- Remove TCODisplay component from VehicleDetailPage
- Delete TCODisplay.tsx component file
- Remove getTCO method from vehicles API client

Legacy TCO fields moved to ownership-costs feature in #29.
Backend endpoint preserved for future reporting feature.

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

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

frontend/src/features/vehicles/api/vehicles.api.ts

@@ -3,7 +3,7 @@
  */
 
 import { apiClient } from '../../../core/api/client';
-import { Vehicle, CreateVehicleRequest, UpdateVehicleRequest, DecodedVehicleData, TCOResponse } from '../types/vehicles.types';
+import { Vehicle, CreateVehicleRequest, UpdateVehicleRequest, DecodedVehicleData } from '../types/vehicles.types';
 
 // All requests (including dropdowns) use authenticated apiClient
 
@@ -88,13 +88,5 @@ export const vehiclesApi = {
   decodeVin: async (vin: string): Promise<DecodedVehicleData> => {
     const response = await apiClient.post('/vehicles/decode-vin', { vin });
     return response.data;
-  },
-
-  /**
-   * Get Total Cost of Ownership data for a vehicle
-   */
-  getTCO: async (vehicleId: string): Promise<TCOResponse> => {
-    const response = await apiClient.get(`/vehicles/${vehicleId}/tco`);
-    return response.data;
   }
 };