feat(mobile): Skia wave, wave player view, themes and playback settings (M5)

- My Wave is rendered with react-native-skia on the UI thread; physics
  and colour helpers moved to @pipu/core (wave-anim) and shared with web.
- Full-screen player honours ui_prefs.mobile_player (cover / wave).
- Theme switching (dark / light / system) via a theme context and
  useColors() across all screens.
- Profile: theme, wave variant, player view, sound quality sheet
  (Wi-Fi / mobile / downloads), recent-tracks cache clearing on next
  cold start, and a change-password sheet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/mobile/src/lib/prefs.ts

@@ -0,0 +1,67 @@
+import * as FileSystem from 'expo-file-system';
+import * as SecureStore from 'expo-secure-store';
+
+export type Quality = 'original' | 'high' | 'medium' | 'low';
+export const QUALITIES: readonly Quality[] = ['original', 'high', 'medium', 'low'];
+
+/** Качество звука по типу сети и для загрузок (настройка устройства, на сервер не уходит). */
+export interface QualityPrefs {
+  wifi: Quality;
+  cellular: Quality;
+  download: Quality;
+}
+
+const QUALITY_KEY = 'pipu.quality';
+const CLEAR_CACHE_KEY = 'pipu.cache.clear';
+const DEFAULT_QUALITY: QualityPrefs = { wifi: 'high', cellular: 'medium', download: 'high' };
+
+let quality: QualityPrefs = DEFAULT_QUALITY;
+let loaded: Promise<void> | null = null;
+const listeners = new Set<() => void>();
+
+export const qualityPrefs = {
+  get: () => quality,
+  subscribe(fn: () => void) {
+    listeners.add(fn);
+    return () => listeners.delete(fn);
+  },
+  async load(): Promise<QualityPrefs> {
+    loaded ??= SecureStore.getItemAsync(QUALITY_KEY)
+      .then((raw) => {
+        if (raw) quality = { ...DEFAULT_QUALITY, ...(JSON.parse(raw) as Partial<QualityPrefs>) };
+      })
+      .catch(() => undefined);
+    await loaded;
+    return quality;
+  },
+  async set(patch: Partial<QualityPrefs>) {
+    quality = { ...quality, ...patch };
+    for (const fn of listeners) fn();
+    await SecureStore.setItemAsync(QUALITY_KEY, JSON.stringify(quality));
+  },
+};
+
+/**
+ * Кэш недавних стримов ExoPlayer (KotlinAudio кладёт его в `cacheDir/TrackPlayer`). Пока сервис плеера жив,
+ * SimpleCache держит индекс в памяти — поэтому очистка откладывается до следующего холодного запуска.
+ */
+const PLAYER_CACHE = `${FileSystem.cacheDirectory}TrackPlayer`;
+
+export const playerCache = {
+  async size(): Promise<number> {
+    const info = await FileSystem.getInfoAsync(PLAYER_CACHE, { size: true }).catch(() => null);
+    return info?.exists ? (info.size ?? 0) : 0;
+  },
+  async requestClear() {
+    await SecureStore.setItemAsync(CLEAR_CACHE_KEY, '1');
+  },
+  async clearPending(): Promise<boolean> {
+    return (await SecureStore.getItemAsync(CLEAR_CACHE_KEY)) === '1';
+  },
+  /** Вызывается до setupPlayer, когда сервис ещё не запущен. */
+  async clearIfRequested() {
+    if (!(await this.clearPending())) return;
+    await FileSystem.deleteAsync(PLAYER_CACHE, { idempotent: true }).catch(() => undefined);
+    await SecureStore.deleteItemAsync(CLEAR_CACHE_KEY);
+  },
+};