feat: implement multi-city support with city management features

- Added a new cities table to the database to manage multiple cities independently.
- Created a middleware to resolve city context based on X-City-Id header.
- Updated routes and services to handle city-specific data for routes, stops, and alerts.
- Implemented a CityContext in the frontend to manage active city state and provide city data across the application.
- Added a CitySelector component for users to switch between cities.
- Created a CitiesPage for admins to manage cities, including adding new cities with validation.
- Updated various components and pages to reflect the active city context, ensuring data is displayed correctly based on the selected city.
- Enhanced the schedule import functionality to restrict imports based on the active city.

backend/src/routes/api.js

@@ -13,8 +13,14 @@ const telemetryController = require('../controllers/telemetryController');
 const passengerTelemetryController = require('../controllers/passengerTelemetryController');
 const { createPassengerTelemetryRateLimiter } = require('../middleware/passengerTelemetryRateLimiter');
 const { authenticateToken, requireAdmin } = require('../middleware/auth');
+const { resolveCity } = require('../middleware/city');
 const qualityController = require('../controllers/qualityController');
 
+// City catalogue is global. Every transport-data endpoint below receives a
+// verified city context from X-City-Id (or falls back to the legacy Polotsk city).
+router.use('/cities', require('./cities'));
+router.use(resolveCity);
+
 router.use('/schedule-import', require('./scheduleImport'));
 router.get('/quality', authenticateToken, requireAdmin, qualityController.getReport.bind(qualityController));