feat(11-03): add site_id and site_name to DeviceResponse

- Add site_id (Optional[UUID]) and site_name (Optional[str]) to backend DeviceResponse schema
- Include site fields in _build_device_response helper
- Add selectinload(Device.site) to _device_with_relations for eager loading
- Add site_id and site_name to frontend DeviceResponse interface

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -306,6 +306,8 @@ export interface DeviceResponse {
   tls_mode: string
   tags: DeviceTagRef[]
   groups: DeviceGroupRef[]
+  site_id: string | null
+  site_name: string | null
   created_at: string
 }