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/search.py

@@ -1,6 +1,6 @@
 from netbox.search import SearchIndex, register_search
 
-from .models import ConceptDevice, RackConcept
+from .models import ConceptCable, ConceptComponent, ConceptDevice, RackConcept
 
 
 @register_search
@@ -25,3 +25,25 @@ class ConceptDeviceIndex(SearchIndex):
         ('comments', 5000),
     )
     display_attrs = ('concept', 'status', 'device_type', 'role', 'description')
+
+
+@register_search
+class ConceptComponentIndex(SearchIndex):
+    model = ConceptComponent
+    fields = (
+        ('name', 100),
+        ('label', 110),
+        ('description', 500),
+    )
+    display_attrs = ('device', 'component_type', 'port_type')
+
+
+@register_search
+class ConceptCableIndex(SearchIndex):
+    model = ConceptCable
+    fields = (
+        ('label', 100),
+        ('description', 500),
+        ('comments', 5000),
+    )
+    display_attrs = ('status', 'type', 'description')