Add network map UX and theme support.

Introduce network map view/components with filtering and positioning, expand contacts/map backend fields and migrations, and add a persistent light/dark theme toggle with graph label color updates for readability.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/contacts/urls.py

@@ -9,6 +9,8 @@ router.register('relations', views.RelationViewSet)
 urlpatterns = [
     path('', include(router.urls)),
     path('graph/', views.graph_data),
+    path('network-map-graph/', views.network_map_graph),
     path('relation-types/', views.relation_types),
+    path('network-map-choices/', views.network_map_choices),
     path('import/', views.import_contacts),
 ]