feat(subsonic): per-server music folder filter and sidebar picker

Apply musicFolderId across Subsonic requests, bump a filter version so library views reload, and add a fixed-position sidebar dropdown (with capped height when there are many folders).

src/locales/zh.ts

@@ -23,6 +23,9 @@ export const zhTranslation = {
     genres: '流派',
     playlists: '播放列表',
     radio: '网络电台',
+    libraryScope: '资料库范围',
+    libraryScopeHint: '浏览整个服务器目录或仅单个媒体文件夹。',
+    allLibraries: '所有资料库',
   },
   home: {
     hero: '精选',