fix(api): typed URLs and accurate response schemas

- Routers use path converters (use_regex_path=False): computes, instances
  and flavors take <int:...> ids, so non-numeric ids get 404 and
  drf-spectacular derives the parameter types itself.
- Each method declares what it really returns: detail serializers,
  a shared StatusSerializer for status-only replies, no request body for
  actions. Instance properties used by the details serializer get return
  type hints.
- The create-instance API drops the firmware field. Its only accepted
  value was "" (BIOS), which produced an empty, invalid enum, and the
  UEFI branch behind it was unreachable. Clients that still send it are
  unaffected; DRF ignores unknown fields.

The schema now passes spectacular --validate --fail-on-warn; a test
keeps it that way.

interfaces/api/viewsets.py

@@ -14,6 +14,7 @@ class InterfaceViewSet(viewsets.ViewSet):
     """
 
     permission_classes = [IsSuperUser]
+    serializer_class = InterfacesSerializer
     
     def list(self, request, compute_pk=None):
         queryset = []