feat: add fleet-wide fuel and maintenance stats endpoints

Backend:
FuelService + FuelController:
- Added getFleetFuelStats() aggregating all vehicles
- Route: GET /api/fuel/stats (before :vehicleId route)
- Returns: totalCost, totalLiters, totalPurchases, averagePricePerLiter

MaintenanceService + MaintenanceController:
- Added getFleetMaintenanceStats() aggregating all vehicles
- Route: GET /api/maintenance/stats (before :vehicleId route)
- Returns: totalCost, numberOfMaintenanceItems, averageCostPerMaintenance, costByType

Both endpoints aggregate over past 12 months (customizable via query param).

Enables dashboard to show fleet-wide operating costs.

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

apps/edr-freight-api/src/modules/maintenance/maintenance.controller.ts

@@ -38,6 +38,12 @@ export class MaintenanceController {
     return this.maintenanceService.getMaintenanceHistory(vehicleId);
   }
 
+  @Get('stats')
+  @ApiOperation({ summary: 'Get fleet-wide maintenance statistics' })
+  async getFleetStats() {
+    return this.maintenanceService.getFleetMaintenanceStats();
+  }
+
   @Get('stats/:vehicleId')
   @ApiOperation({ summary: 'Get maintenance statistics' })
   async getStats(@Param('vehicleId') vehicleId: string) {