feat(folders): add rename, missing-folder recovery, and right-click context menu

- Backend: new `rename_folder` command (updates display name only, not path)
  and `update_folder_path` command (rewrites image paths in DB before reindexing
  so thumbnails/embeddings are not regenerated unnecessarily)
- DB: `rename_folder` and `update_folder_path` helpers; `scan_error` column on
  folders table to surface indexing failures without silently dropping images
- Store: `renameFolder` and `updateFolderPath` actions
- Sidebar: right-click context menu on each folder row (Reindex, Rename, Locate
  Folder, Remove from app); inline rename input on Enter/Escape/blur; missing-
  folder recovery banner with Locate/Remove; hover icon buttons (reindex + remove
  with Confirm/Cancel) preserved alongside the context menu

src/store.ts

@@ -287,6 +287,7 @@ interface GalleryState {
   addFolder: (path: string) => Promise<void>;
   removeFolder: (folderId: number) => Promise<void>;
   reindexFolder: (folderId: number) => Promise<void>;
+  renameFolder: (folderId: number, newName: string) => Promise<void>;
   updateFolderPath: (folderId: number, newPath: string) => Promise<void>;
   selectFolder: (folderId: number | null) => void;
   loadImages: (reset?: boolean) => Promise<void>;
@@ -671,6 +672,11 @@ export const useGalleryStore = create<GalleryState>((set, get) => ({
     await loadBackgroundJobProgress();
   },
 
+  renameFolder: async (folderId, newName) => {
+    await invoke("rename_folder", { folderId, newName });
+    await get().loadFolders();
+  },
+
   updateFolderPath: async (folderId, newPath) => {
     const { loadFolders, loadBackgroundJobProgress } = get();
     await invoke("update_folder_path", { folderId, newPath });