feat: add multi-city representation support and domain context resolution

- Created migration to add representation_cities table and domain, is_global fields to representations.
- Implemented SiteContextController to resolve domain to site context (city | representation | unknown).
- Developed DomainContext and DomainContextResolver services for domain mapping.
- Added tests for DomainContextResolver and commission logic based on domain ownership.

docs/api/admin.md

@@ -742,7 +742,7 @@ List all representations.
 | `page` | integer | ❌ | Default: 1 |
 | `limit` | integer | ❌ | Default: 15 |
 | `search` | string | ❌ | Search by name or mobile (representation's or linked user's) |
-| `city_id` | integer | ❌ | Filter by city |
+| `city_id` | integer | ❌ | Filter by city (عضویت در شهرهای چندگانه‌ی نماینده — `representation_cities`) |
 
 ### Response `200`
 Paginated representation list. Each item:
@@ -752,14 +752,19 @@ Paginated representation list. Each item:
   "uuid": "...",
   "full_name": "حامد حسینی",
   "mobile_number": "09120671756",
+  "domain": "x-nobat.ir",
+  "is_global": true,
   "city_id": 132,
-  "city": "یزد",
+  "city_ids": [132, 108],
+  "cities": [{ "id": 132, "name": "یزد" }, { "id": 108, "name": "تهران" }],
+  "city": "یزد، تهران",
   "commission_percent": 10.0,
   "wallet_balance": 0,
   "is_active": true,
   "created_at": "2026-06-18T..."
 }
 ```
+> `city_id` = اولین شهر (BC)؛ `city` = نام شهرها با «،». `is_global=true` یعنی نماینده سراسری (badge در پنل).
 
 > `mobile_number` falls back to the linked user's mobile when the representation's own `mobile_number` column is empty.