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/plugins/base.py

@@ -0,0 +1,48 @@
+"""Plugin platform base classes and registry."""
+
+from abc import ABC, abstractmethod
+from typing import List
+
+from django.conf import settings
+from django.urls import URLPattern
+
+
+class Plugin(ABC):
+    id: str = ''
+    version: str = '1.0.0'
+    min_core_version: str = '1.0.0'
+    permissions: List[str] = []
+
+    @abstractmethod
+    def urlpatterns(self) -> List[URLPattern]:
+        pass
+
+    def installed_apps(self) -> List[str]:
+        return []
+
+
+_REGISTRY: dict[str, Plugin] = {}
+
+
+def register_plugin(plugin: Plugin) -> None:
+    _REGISTRY[plugin.id] = plugin
+
+
+def get_plugin(plugin_id: str) -> Plugin | None:
+    return _REGISTRY.get(plugin_id)
+
+
+def get_enabled_plugins() -> List[Plugin]:
+    enabled = getattr(settings, 'ENABLED_PLUGINS', [])
+    return [_REGISTRY[pid] for pid in enabled if pid in _REGISTRY]
+
+
+def plugin_urlpatterns() -> List[URLPattern]:
+    from django.urls import path, include
+
+    patterns: List[URLPattern] = []
+    for plugin in get_enabled_plugins():
+        patterns.append(
+            path(f'plugins/{plugin.id}/', include((plugin.urlpatterns(), plugin.id)))
+        )
+    return patterns