fix(sidebar): keep the recipes storage dir out of folder management

The default recipes dir (<first lora root>/recipes) is auto-created by the
recipe scanner and recorded by the model-root walks as an empty folder, so
it showed up in the folder sidebar — and since recipe files are not model
weight files, the folder delete endpoint's model_count check let a
right-click delete wipe the whole recipe library via shutil.rmtree.

- scan walks (full scan, reconcile, all-folders backfill) no longer descend
  into the effective recipes dir, and get_all_folders() filters it out of
  snapshots persisted before the exclusion existed
- delete_folder/rename_folder refuse the recipes dir and any ancestor of
  it with code "protected"
- the delete modal renders a protected state (confirm hidden, per-row
  checkbox disabled) instead of a deletable 'no models' prediction
- RecipeScanner.recipes_dir now shares the side-effect-free resolver in
  py/utils/recipes_paths.py

tests/frontend/components/sidebarManager.folderManagement.test.js

@@ -794,6 +794,21 @@ describe('SidebarManager folder deletion', () => {
     expect(confirmBtn().style.display).toBe('none');
   });
 
+  it('blocks the delete when the folder holds the recipe library', async () => {
+    const protectedError = Object.assign(new Error('recipe library'), { code: 'protected' });
+    const apiClient = createApiClient({
+      deleteFolder: vi.fn().mockRejectedValue(protectedError),
+    });
+    const manager = createManager(apiClient);
+    manager.nonEmptyFolders = new Set(['', 'full']);
+
+    await manager.showDeleteFolderModal('empty');
+
+    const modal = document.getElementById('deleteFolderModal');
+    expect(modal.dataset.state).toBe('protected');
+    expect(confirmBtn().style.display).toBe('none');
+  });
+
   it('keeps the confirm button disabled until the check settles', async () => {
     let release;
     const apiClient = createApiClient({