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/fuel/fuel.controller.ts

@@ -43,6 +43,12 @@ export class FuelController {
     return this.fuelService.getMonthlyConsumption(vehicleId, new Date(month));
   }
 
+  @Get('stats')
+  @ApiOperation({ summary: 'Get fleet-wide fuel statistics' })
+  async getFleetFuelStats(@Query('months') months: number = 12) {
+    return this.fuelService.getFleetFuelStats(months);
+  }
+
   @Get('stats/:vehicleId')
   @ApiOperation({ summary: 'Get fuel statistics for vehicle' })
   async getVehicleFuelStats(