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>

frontend/src/plugins/_template/index.js

@@ -0,0 +1,18 @@
+/**
+ * Template for new frontend plugins.
+ * Copy to frontend/src/plugins/<your-id>/ and register in bootstrapPlugins.js loaders.
+ */
+import { registerPlugin } from '../../core/pluginRegistry'
+
+export function registerMyPlugin() {
+  registerPlugin({
+    id: 'my-plugin',
+    version: '1.0.0',
+    minCoreVersion: '1.0.0',
+    permissions: [],
+    routes: [],
+    navItems: [],
+  })
+}
+
+// registerMyPlugin()