Add plugin platform with modular backend and frontend registry.

Split graph/import/meta into Django apps, add API v1 with OpenAPI and pytest, and introduce plugin registry with the tags reference plugin on both FE and BE.

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

backend/contacts/urls.py

@@ -1,32 +1,6 @@
+"""Legacy /api/ routes — mirrors v1 for backward compatibility."""
 from django.urls import path, include
-from rest_framework.routers import DefaultRouter
-from . import views
-
-router = DefaultRouter()
-router.register('contacts', views.ContactViewSet)
-router.register('relations', views.RelationViewSet)
-router.register('network-maps', views.NetworkMapViewSet)
 
 urlpatterns = [
-    path('', include(router.urls)),
-    path(
-        'network-maps/<int:map_pk>/memberships/',
-        views.NetworkMapMembershipViewSet.as_view({'get': 'list', 'post': 'create'}),
-        name='network-map-memberships-list',
-    ),
-    path(
-        'network-maps/<int:map_pk>/memberships/<int:pk>/',
-        views.NetworkMapMembershipViewSet.as_view({
-            'get': 'retrieve',
-            'patch': 'partial_update',
-            'put': 'update',
-            'delete': 'destroy',
-        }),
-        name='network-map-memberships-detail',
-    ),
-    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),
+    path('', include('api.v1.urls')),
 ]