feat(sidebar): multi-level playlist folders with tree and navigation views (#2017)

Group playlists into folders using a configurable separator (default '/').
Three view modes:
- Single: first-level grouping only (original behavior)
- Tree: full recursive nesting with connecting lines (configurable indent and line color)
- Navigation: drill-down view with stacked breadcrumb chain

Folders are sorted before playlists at every level. New settings render as
indented sub-options under the master 'Enable folders' toggle.

src/renderer/features/settings/components/settings-section.tsx

@@ -8,6 +8,7 @@ import { TextTitle } from '/@/shared/components/text-title/text-title';
 export type SettingOption = {
     control: ReactNode;
     description: ReactNode | string;
+    indent?: boolean;
     isHidden?: boolean;
     note?: string;
     title: string;