feat(sidebar): show empty folders and create folders from the sidebar (#999)

Empty folders (tracked in the scan-recorded all_folders list, same source
the move/download destination picker uses) can now be surfaced in the
folder sidebar via a view-options toggle, dimmed when their subtree holds
no models. Folders can be created directly from the sidebar through a new
POST /api/lm/{prefix}/create-folder endpoint with library-root
containment checks; the scanner records the new directory incrementally
so the tree reflects it without a rescan.

The sidebar header moves its view toggles (tree/list, recursive, empty
folders) into a "..." menu to fit the new create-folder button.

py/routes/handlers/model_handlers.py

@@ -2479,6 +2479,26 @@ class ModelMoveHandler:
         self._move_service = move_service
         self._logger = logger
 
+    async def create_folder(self, request: web.Request) -> web.Response:
+        try:
+            data = await request.json()
+        except Exception:
+            return web.json_response(
+                {"success": False, "error": "Invalid JSON body"}, status=400
+            )
+        try:
+            folder_path = data.get("folder_path")
+            if not folder_path:
+                return web.json_response(
+                    {"success": False, "error": "Folder path is required"}, status=400
+                )
+            result = await self._move_service.create_folder(folder_path)
+            status = 200 if result.get("success") else 400
+            return web.json_response(result, status=status)
+        except Exception as exc:
+            self._logger.error("Error creating folder: %s", exc, exc_info=True)
+            return web.json_response({"success": False, "error": str(exc)}, status=500)
+
     async def move_model(self, request: web.Request) -> web.Response:
         try:
             data = await request.json()
@@ -3429,6 +3449,7 @@ class ModelHandlerSet:
             "get_civitai_model_by_hash": self.civitai.get_civitai_model_by_hash,
             "move_model": self.move.move_model,
             "move_models_bulk": self.move.move_models_bulk,
+            "create_folder": self.move.create_folder,
             "auto_organize_models": self.auto_organize.auto_organize_models,
             "get_auto_organize_progress": self.auto_organize.get_auto_organize_progress,
             "get_model_notes": self.query.get_model_notes,