fix: location navigation uses IDs and pipe separators instead of underscore

Critical fix for product management location selection:
- Country/city callback_data now uses pipe | as separator with
  encodeURIComponent/decodeURIComponent for special chars
- District selection uses location ID (prod_loc_{id}, shop_loc_{id})
  instead of underscore-delimited country_city_district text
- Empty district names now show city name as fallback
- LocationService.getLocationsByCountryAndCity() returns id+district
  for building callback_data with location IDs
- All error handlers in admin product navigation use editOrSendCallback
  to avoid chat clutter
- Routes updated: prod_district_ → prod_loc_, shop_district_ → shop_loc_

This fixes the bug where selecting country/city/district in admin panel
or shop failed because split('_') broke on multi-word names or empty
district values.

src/services/locationService.js

@@ -15,7 +15,14 @@ class LocationService {
 
     static async getDistrictsByCountryAndCity(country, city) {
         return await db.allAsync(
-            'SELECT district FROM locations WHERE country = ? AND city = ? ORDER BY district',
+            'SELECT id, district FROM locations WHERE country = ? AND city = ? ORDER BY district',
+            [country, city]
+        );
+    }
+
+    static async getLocationsByCountryAndCity(country, city) {
+        return await db.allAsync(
+            'SELECT id, country, city, district FROM locations WHERE country = ? AND city = ? ORDER BY district',
             [country, city]
         );
     }