Fix rear-face image-only labels, click-to-add units, cable concept devices

- Fix "images only" leaving plain labels visible on faces where a
  device has no image for that side (e.g. no rear_image set): the
  view selector now hides every plain label outright in that mode,
  not just the ones an image happens to sit on top of.
- Remove the "Add planned device" button from the elevation card.
  Empty units are now click targets themselves - clicking one opens
  the add-device form pre-filled with that position and face, exactly
  like a real rack's elevation. Occupancy is computed per unit per
  face from the existing device blocks.
- Add cabling for concept devices: ConceptComponent (interfaces,
  front/rear ports, power ports/outlets, console ports) and
  ConceptCable (a connection between two components, restricted to
  devices in the same concept). components.sync_components()
  populates a device's components from its device type's templates,
  including the front/rear port pass-through mapping copied from
  DeviceType.port_mappings - so a device with front/rear port
  templates (a patch panel being the common case) behaves exactly
  like a real one, without hardcoding anything role-specific.
  Placeholder devices without a device type get components added by
  hand. Full CRUD views, tables, filtersets, API endpoints and a
  "Connect" action wired in from the device detail page.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

netbox_rack_concept/api/views.py

@@ -11,10 +11,10 @@ from netbox.api.viewsets import NetBoxModelViewSet
 from .. import filtersets
 from .. import deploy as deploy_utils
 from ..elevation import get_elevations
-from ..models import ConceptDevice, RackConcept
+from ..models import ConceptCable, ConceptComponent, ConceptDevice, RackConcept
 from .serializers import (
-    ConceptDeploySerializer, ConceptDeviceSerializer, MergeConceptsSerializer, RackConceptCloneSerializer,
-    RackConceptSerializer, RackCopySerializer,
+    ConceptCableSerializer, ConceptComponentSerializer, ConceptDeploySerializer, ConceptDeviceSerializer,
+    MergeConceptsSerializer, RackConceptCloneSerializer, RackConceptSerializer, RackCopySerializer,
 )
 
 __all__ = (
@@ -204,3 +204,17 @@ class ConceptDeviceViewSet(NetBoxModelViewSet):
     )
     serializer_class = ConceptDeviceSerializer
     filterset_class = filtersets.ConceptDeviceFilterSet
+
+
+class ConceptComponentViewSet(NetBoxModelViewSet):
+    queryset = ConceptComponent.objects.prefetch_related('tags').select_related('device', 'device__concept')
+    serializer_class = ConceptComponentSerializer
+    filterset_class = filtersets.ConceptComponentFilterSet
+
+
+class ConceptCableViewSet(NetBoxModelViewSet):
+    queryset = ConceptCable.objects.prefetch_related('tags').select_related(
+        'termination_a', 'termination_a__device', 'termination_b', 'termination_b__device'
+    )
+    serializer_class = ConceptCableSerializer
+    filterset_class = filtersets.ConceptCableFilterSet