feat(folder-browser): keyboard nav, context menus, now-playing path UX

Adds full keyboard navigation (arrow keys, Enter, Ctrl+Enter for context menu) across Folder Browser columns. Context menus for all row types with keyboard-operable submenus and star-rating control via arrow keys + Enter. Now-playing path is visually emphasized and stays stable; rebuilds on hotkey re-invoke or active-path follow-along. Adaptive column layout for deep trees with right-side visibility priority. New configurable 'Open Folder Browser' keybinding. StarRating animation sync for keyboard-driven changes. All 7 locales updated.

src/store/keybindingsStore.ts

@@ -10,6 +10,7 @@ export type KeyAction =
   | 'seek-forward'
   | 'seek-backward'
   | 'toggle-queue'
+  | 'open-folder-browser'
   | 'fullscreen-player'
   | 'native-fullscreen';
 
@@ -25,6 +26,7 @@ export const DEFAULT_BINDINGS: Bindings = {
   'seek-forward':      null,
   'seek-backward':     null,
   'toggle-queue':      null,
+  'open-folder-browser': null,
   'fullscreen-player': null,
   'native-fullscreen': 'F11',
 };