feat: Implement recursive storage listing and directory browsing for backups, and add a migration option to fix cross-filters.

backend/src/api/routes/storage.py

@@ -36,6 +36,7 @@ router = APIRouter(tags=["storage"])
 async def list_files(
     category: Optional[FileCategory] = None,
     path: Optional[str] = None,
+    recursive: bool = False,
     plugin_loader=Depends(get_plugin_loader),
     _ = Depends(has_permission("plugin:storage", "READ"))
 ):
@@ -43,7 +44,7 @@ async def list_files(
         storage_plugin: StoragePlugin = plugin_loader.get_plugin("storage-manager")
         if not storage_plugin:
             raise HTTPException(status_code=500, detail="Storage plugin not loaded")
-        return storage_plugin.list_files(category, path)
+        return storage_plugin.list_files(category, path, recursive)
 # [/DEF:list_files:Function]
 
 # [DEF:upload_file:Function]
@@ -143,4 +144,4 @@ async def download_file(
             raise HTTPException(status_code=400, detail=str(e))
 # [/DEF:download_file:Function]
 
-# [/DEF:storage_routes:Module]
+# [/DEF:storage_routes:Module]