fix: use vehicle initial_km as start_km for first trip record

When no trips exist for a vehicle, the last-km endpoint now returns
the vehicle's initial_km instead of 0, matching the PHP behavior:
COALESCE(MAX(end_km), vehicle.initial_km, 0)

Also fixed ordering from id DESC to end_km DESC for correctness.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/routes/admin/trips.ts

@@ -108,15 +108,28 @@ export default async function tripsRoutes(fastify: FastifyInstance): Promise<voi
   });
 
   // GET /api/admin/trips/last-km/:vehicleId
+  // Matches PHP: COALESCE(MAX(end_km), vehicle.initial_km, 0)
   fastify.get<{ Params: { vehicleId: string } }>('/last-km/:vehicleId', { preHandler: requireAuth }, async (request, reply) => {
     const vehicleId = parseInt(request.params.vehicleId, 10);
     if (isNaN(vehicleId)) return error(reply, 'Neplatné ID vozidla', 400);
-    const lastTrip = await prisma.trips.findFirst({
-      where: { vehicle_id: vehicleId },
-      orderBy: { id: 'desc' },
-      select: { end_km: true },
-    });
-    return success(reply, { last_km: lastTrip ? Number(lastTrip.end_km) : 0 });
+
+    const [lastTrip, vehicle] = await Promise.all([
+      prisma.trips.findFirst({
+        where: { vehicle_id: vehicleId },
+        orderBy: { end_km: 'desc' },
+        select: { end_km: true },
+      }),
+      prisma.vehicles.findUnique({
+        where: { id: vehicleId },
+        select: { initial_km: true },
+      }),
+    ]);
+
+    const lastKm = lastTrip
+      ? Number(lastTrip.end_km)
+      : Number(vehicle?.initial_km ?? 0);
+
+    return success(reply, { last_km: lastKm });
   });
 
   fastify.post('/', { preHandler: requireAuth }, async (request, reply) => {