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/pages/Settings.tsx

@@ -1541,6 +1541,7 @@ export default function Settings() {
                 ['seek-forward',      t('settings.shortcutSeekForward')],
                 ['seek-backward',     t('settings.shortcutSeekBackward')],
                 ['toggle-queue',      t('settings.shortcutToggleQueue')],
+                ['open-folder-browser', t('settings.shortcutOpenFolderBrowser', { folderBrowser: t('sidebar.folderBrowser') })],
                 ['fullscreen-player', t('settings.shortcutFullscreenPlayer')],
                 ['native-fullscreen', t('settings.shortcutNativeFullscreen')],
               ] as [KeyAction, string][]).map(([action, label]) => {