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/serializers.py

@@ -11,9 +11,11 @@ from tenancy.api.serializers import TenantGroupSerializer, TenantSerializer
 from tenancy.models import Tenant
 
 from ..choices import ConceptStatusChoices
-from ..models import ConceptDeployment, ConceptDevice, RackConcept
+from ..models import ConceptCable, ConceptComponent, ConceptDeployment, ConceptDevice, RackConcept
 
 __all__ = (
+    'ConceptCableSerializer',
+    'ConceptComponentSerializer',
     'ConceptDeploySerializer',
     'ConceptDeploymentSerializer',
     'ConceptDeviceSerializer',
@@ -81,6 +83,38 @@ class ConceptDeploymentSerializer(serializers.ModelSerializer):
         fields = ('id', 'rack', 'rack_name', 'device_count', 'user', 'created')
 
 
+class ConceptComponentSerializer(NetBoxModelSerializer):
+    url = serializers.HyperlinkedIdentityField(
+        view_name='plugins-api:netbox_rack_concept-api:conceptcomponent-detail'
+    )
+    device = ConceptDeviceSerializer(nested=True)
+    is_connected = serializers.BooleanField(read_only=True)
+
+    class Meta:
+        model = ConceptComponent
+        fields = (
+            'id', 'url', 'display_url', 'display', 'device', 'component_type', 'name', 'label', 'port_type',
+            'positions', 'color', 'description', 'is_connected', 'tags', 'custom_fields', 'created', 'last_updated',
+        )
+        brief_fields = ('id', 'url', 'display', 'name', 'component_type', 'device')
+
+
+class ConceptCableSerializer(NetBoxModelSerializer):
+    url = serializers.HyperlinkedIdentityField(
+        view_name='plugins-api:netbox_rack_concept-api:conceptcable-detail'
+    )
+    termination_a = ConceptComponentSerializer(nested=True)
+    termination_b = ConceptComponentSerializer(nested=True)
+
+    class Meta:
+        model = ConceptCable
+        fields = (
+            'id', 'url', 'display_url', 'display', 'termination_a', 'termination_b', 'status', 'type', 'color',
+            'label', 'description', 'comments', 'tags', 'custom_fields', 'created', 'last_updated',
+        )
+        brief_fields = ('id', 'url', 'display', 'label', 'termination_a', 'termination_b')
+
+
 #
 # Action payloads
 #