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/clinic.md

@@ -196,6 +196,7 @@ List clinics with pagination.
 | `city` | integer | ❌ | City id — filters by the **clinic address's** city |
 | `state` | integer | ❌ | Province id — filters by the **clinic address's** province |
 | `specialty` | integer | ❌ | Specialty id |
+| `domain` | string | ❌ | دامنه‌ی سایتِ درخواست‌کننده. اگر دامنه‌ی یک **نماینده سراسری** باشد، فقط کلینیک‌های همان نماینده برمی‌گردند و `city`/`state` نادیده گرفته می‌شوند؛ دامنه شهری/ناشناخته اثری ندارد |
 
 > `city`/`state` are matched against the clinic's address (`DoctorAddress` linked by `clinic_id`), not a field on the clinic itself.