Refactor backend and frontend cleanup paths

backend/storage/cloud_backend_factory.py

@@ -0,0 +1,33 @@
+"""Factory for user-scoped cloud storage backends."""
+
+
+def build_cloud_backend(provider: str, credentials: dict):
+    if provider == "google_drive":
+        from storage.google_drive_backend import GoogleDriveBackend  # lazy import
+
+        return GoogleDriveBackend(credentials)
+
+    if provider == "onedrive":
+        from storage.onedrive_backend import OneDriveBackend  # lazy import
+
+        return OneDriveBackend(credentials)
+
+    if provider == "nextcloud":
+        from storage.nextcloud_backend import NextcloudBackend  # lazy import
+
+        return NextcloudBackend(
+            credentials["server_url"],
+            credentials["username"],
+            credentials["password"],
+        )
+
+    if provider == "webdav":
+        from storage.webdav_backend import WebDAVBackend  # lazy import
+
+        return WebDAVBackend(
+            credentials["server_url"],
+            credentials["username"],
+            credentials["password"],
+        )
+
+    raise ValueError(f"Unknown provider: {provider}")