feat(lyrics): configurable sources with drag-to-reorder + feat(audio): ReplayGain pre-gain & fallback

Lyrics Sources:
- Replace lyricsServerFirst + enableNeteaselyrics toggles with a new
  Settings section — three sources (Server, LRCLIB, Netease) each
  individually toggled and drag-reorderable via psy-drop DnD
- useLyrics.ts iterates sources in user-defined order, skipping disabled
  ones; embedded SYLT from local files still wins unconditionally
- onRehydrateStorage migration from legacy fields on first load

ReplayGain Pre-Gain:
- New authStore fields: replayGainPreGainDb (0…+6 dB) and
  replayGainFallbackDb (-6…0 dB, untagged / radio)
- audio.rs compute_gain applies pre_gain_db and fallback_db
- Settings sliders under ReplayGain mode selector
- Radio HTML5 volume scaled by fallbackDb factor on playRadio

i18n(ru): incorporate PR #148 translation improvements (kilyabin)
All 7 locales updated for new keys.

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

src/locales/zh.ts

@@ -485,6 +485,11 @@ export const zhTranslation = {
     lyricsServerFirstDesc: '先查询服务器提供的歌词（内嵌标签、sidecar 文件），再查询 LRCLIB。禁用则优先使用 LRCLIB。',
     enableNeteaselyrics: '网易云音乐歌词',
     enableNeteaselyricsDesc: '当服务器和 LRCLIB 均无结果时，使用网易云音乐作为最终歌词来源。对亚洲及国际音乐覆盖最佳。',
+    lyricsSourcesTitle: '歌词来源',
+    lyricsSourcesDesc: '选择要查询的歌词来源及其顺序。拖动以排序。已禁用的来源将被跳过。',
+    lyricsSourceServer: '服务器',
+    lyricsSourceLrclib: 'LRCLIB',
+    lyricsSourceNetease: '网易云音乐',
     downloadsTitle: 'ZIP 导出与归档',
     downloadsFolderDesc: '将专辑以 ZIP 文件下载到电脑时的目标文件夹。',
     downloadsDefault: '默认下载文件夹',
@@ -568,6 +573,8 @@ export const zhTranslation = {
     replayGainMode: '模式',
     replayGainTrack: '曲目',
     replayGainAlbum: '专辑',
+    replayGainPreGain: '预增益（有标签文件）',
+    replayGainFallback: '回退增益（无标签 / 收音机）',
     crossfade: '交叉淡入淡出',
     crossfadeDesc: '曲目间淡入淡出',
     crossfadeSecs: '{{n}} 秒',