fix(bot): issue #129 — missing shop_district_/shop_subcategory_ handlers, answerCallbackQuery timing, state.location pipe format

- Register shop_district_ (handleDistrictBack) + shop_subcategory_ (handleSubcategorySelection) in routes.js — Back button in empty categories now works
- state.location pipe-delimited with encodeURIComponent — multi-word names (Saint Petersburg) no longer break nav
- answerCallbackQuery moved to start of callback handling — no stuck spinner
- Empty city fallback (district_unknown) in Select district
- Guard against stale underscore-format state.location
- 48 tests pass; bump v1.2.4

src/i18n/locales/es.json

@@ -60,7 +60,8 @@
     "mono_product": "📦 Producto Digital",
     "infinite_stock": "∞ Siempre disponible",
     "no_description": "Sin descripción",
-    "no_photo": "Sin foto disponible"
+    "no_photo": "Sin foto disponible",
+    "district_unknown": "Desconocido"
   },
   "purchase": {
     "summary": "🛒 Resumen de compra:",