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/tests/test_meta_api.py

@@ -0,0 +1,20 @@
+import pytest
+
+
+@pytest.mark.django_db
+def test_meta_choices(api_client):
+    response = api_client.get('/api/v1/meta/choices/')
+    assert response.status_code == 200
+    data = response.data
+    assert 'relation_types' in data
+    assert 'life_spheres' in data
+    assert 'network_circles' in data
+    assert 'interaction_intensities' in data
+    assert any(x['value'] == 'friend' for x in data['relation_types'])
+
+
+@pytest.mark.django_db
+def test_relation_types_legacy(api_client):
+    response = api_client.get('/api/v1/relation-types/')
+    assert response.status_code == 200
+    assert len(response.data) >= 1