feat(nav): merge Random Mix & Albums into Build a Mix hub

Replaces two sidebar entries (Random Mix, Random Albums) with a single 'Build a Mix' item (Wand2 icon) at /random. Landing page shows two cards — Mix by Tracks and Mix by Albums — with glow-on-hover. Old routes updated throughout. All 7 locales updated.

src/store/sidebarStore.ts

@@ -12,10 +12,9 @@ export const DEFAULT_SIDEBAR_ITEMS: SidebarItemConfig[] = [
   { id: 'mainstage',     visible: true },
   { id: 'newReleases',   visible: true },
   { id: 'allAlbums',     visible: true },
-  { id: 'randomAlbums',  visible: true },
+  { id: 'randomPicker',  visible: true },
   { id: 'artists',       visible: true },
   { id: 'genres',        visible: true },
-  { id: 'randomMix',     visible: true },
   { id: 'favorites',     visible: true },
   { id: 'playlists',     visible: true },
   { id: 'mostPlayed',    visible: true },