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/pages/VehicleDetailPage.tsx

@@ -16,7 +16,6 @@ import { vehiclesApi } from '../api/vehicles.api';
 import { Card } from '../../../shared-minimal/components/Card';
 import { VehicleForm } from '../components/VehicleForm';
 import { VehicleImage } from '../components/VehicleImage';
-import { TCODisplay } from '../components/TCODisplay';
 import { useFuelLogs } from '../../fuel-logs/hooks/useFuelLogs';
 import { FuelLogResponse, UpdateFuelLogRequest } from '../../fuel-logs/types/fuel-logs.types';
 import { FuelLogEditDialog } from '../../fuel-logs/components/FuelLogEditDialog';
@@ -383,14 +382,6 @@ export const VehicleDetailPage: React.FC = () => {
               </Typography>
             )}
           </Box>
-          {/* TCO Display - right-justified */}
-          <Box sx={{
-            width: { xs: '100%', md: 'auto' },
-            minWidth: { md: 200 },
-            mt: { xs: 2, md: 0 }
-          }}>
-            <TCODisplay vehicleId={vehicle.id} tcoEnabled={vehicle.tcoEnabled} />
-          </Box>
         </Box>
 
         <form className="space-y-4">