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>

backend/app/schemas/device.py

@@ -88,6 +88,8 @@ class DeviceResponse(BaseModel):
     tls_mode: str = "auto"
     tags: list[DeviceTagRef] = []
     groups: list[DeviceGroupRef] = []
+    site_id: Optional[uuid.UUID] = None
+    site_name: Optional[str] = None
     created_at: datetime
 
     model_config = {"from_attributes": True}