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_plugins_api.py

@@ -0,0 +1,27 @@
+import pytest
+
+
+@pytest.mark.django_db
+def test_plugin_manifest(api_client):
+    response = api_client.get('/api/v1/plugins/')
+    assert response.status_code == 200
+    ids = [p['id'] for p in response.data]
+    assert 'tags' in ids
+
+
+@pytest.mark.django_db
+def test_tags_crud(api_client, sample_contact):
+    create = api_client.post(
+        '/api/v1/plugins/tags/contact-tags/',
+        {'contact': sample_contact.id, 'label': 'коллеги'},
+        format='json',
+    )
+    assert create.status_code == 201
+    tag_id = create.data['id']
+
+    listing = api_client.get(f'/api/v1/plugins/tags/contact-tags/?contact_id={sample_contact.id}')
+    assert listing.status_code == 200
+    assert listing.data['count'] == 1
+
+    delete = api_client.delete(f'/api/v1/plugins/tags/contact-tags/{tag_id}/')
+    assert delete.status_code == 204