feat: bg presets in settings, shuffle playlists, remove theme from ExtraTab

- Add 4 live background modes: Орбы, Волны, Частицы, Аврора + Нет
- Settings page shows visual preview cards for each bg mode (persisted)
- Add shuffle button (⇄) to PlaylistCard and FavoritesCard
- Remove accent color picker from ExtraTab (settings page only)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/src/store/bgStore.ts

@@ -0,0 +1,38 @@
+'use client'
+
+import { create } from 'zustand'
+
+export type BgMode = 'orbs' | 'waves' | 'particles' | 'aurora' | 'none'
+
+export interface BgPreset {
+  id: BgMode
+  name: string
+  desc: string
+}
+
+export const BG_PRESETS: BgPreset[] = [
+  { id: 'orbs',      name: 'Орбы',     desc: 'Мягкие цветовые пятна' },
+  { id: 'waves',     name: 'Волны',    desc: 'Звуковые волны снизу' },
+  { id: 'particles', name: 'Частицы',  desc: 'Плавающая сеть точек' },
+  { id: 'aurora',    name: 'Аврора',   desc: 'Северное сияние' },
+  { id: 'none',      name: 'Нет',      desc: 'Чистый фон' },
+]
+
+const KEY = 'pm_bg'
+
+interface BgStore {
+  bgMode: BgMode
+  setBg: (mode: BgMode) => void
+}
+
+export const useBgStore = create<BgStore>((set) => ({
+  bgMode: (() => {
+    if (typeof window === 'undefined') return 'orbs'
+    const saved = localStorage.getItem(KEY) as BgMode | null
+    return saved && BG_PRESETS.some(p => p.id === saved) ? saved : 'orbs'
+  })(),
+  setBg: (mode) => {
+    if (typeof window !== 'undefined') localStorage.setItem(KEY, mode)
+    set({ bgMode: mode })
+  },
+}))