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/__init__.py

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+

backend/plugins/apps.py

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+from django.apps import AppConfig
+
+
+class PluginsConfig(AppConfig):
+    default_auto_field = 'django.db.models.BigAutoField'
+    name = 'plugins'
+
+    def ready(self):
+        import plugins.registry  # noqa: F401

backend/plugins/base.py

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+"""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

backend/plugins/registry.py

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+"""Register built-in plugins."""
+
+from plugins.base import register_plugin
+from plugins_tags.plugin import TagsPlugin
+
+register_plugin(TagsPlugin())

backend/plugins/urls.py

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+from django.urls import path
+
+from . import views
+from .base import plugin_urlpatterns
+
+urlpatterns = [
+    path('plugins/', views.plugin_manifest, name='plugin-manifest'),
+    *plugin_urlpatterns(),
+]

backend/plugins/views.py

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+from django.urls import path
+from rest_framework.decorators import api_view
+from rest_framework.response import Response
+
+from plugins.base import get_enabled_plugins
+
+
+@api_view(['GET'])
+def plugin_manifest(request):
+    """List enabled plugins and their metadata."""
+    return Response([
+        {
+            'id': p.id,
+            'version': p.version,
+            'min_core_version': p.min_core_version,
+            'permissions': p.permissions,
+        }
+        for p in get_enabled_plugins()
+    ])