feat(hub): audio_root wiring, mutually-exclusive players, Settings rework

Five related pieces of polish against the Music app and Settings, all
from the same conversation:

- Music app now requires audio_root, same as Videos requires video_root:
  an empty-state message until one is set, and grouping filtered to only
  what's under it (underAudioRoot, mirroring video-app.js's
  underVideoRoot). Wires the new audio_root/audio_root_ack pair through
  transport.js and group-page.js state the same way video_root already
  flows.
- Starting one player now stops the other — opening a film closes the
  music queue, starting a track closes the video modal. Both used to run
  at once, found live.
- Group Settings reworked: every section but a bare form (invite,
  pair-operator, approve-device) is now collapsible (CollapsibleSection);
  the uploads on/off button is a real toggle switch (ToggleSwitch,
  reused for TMDB/MusicBrainz's enabled switches too, each now with an
  icon + status badge in its header instead of a plain checkbox row);
  and shared directories, the Videos root picker, and the new Music root
  picker are merged into one "Directories" section (RootFolderRow) instead
  of three separate ones scattered down the page — the root pickers only
  show once their app is actually enabled.

1 files changed, 9 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
index 236747e..a26062d 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/locales/zh-CN.js
@@ -155,6 +155,7 @@ export default {
   'video.mode_flat': '平铺列表',
   'video.empty': '未找到视频。',
   'video.no_root_configured': '此群组尚未设置视频根目录 — 操作员可以在设置中选择一个。',
+  'music.no_root_configured': '此群组尚未设置音乐根目录 — 操作员可以在设置中选择一个。',
   'video.director': '导演',
   'video.specials': '特别篇',
   'video.season_n': '第 {n} 季',
@@ -624,6 +625,14 @@ export default {
   'settings_node.video_root_save': '保存',
   'settings_node.video_root_change_confirm': '更改视频根目录会替换每位成员在"视频"标签页中看到的内容。是否继续？',
 
+  'settings_node.audio_root_title': '音乐根目录',
+  'settings_node.audio_root_hint': '该文件夹（或子文件夹）将作为此群组“音乐”应用的入口。在选择之前，“音乐”中不会显示任何内容，也不会读取任何标签/封面信息。',
+  'settings_node.audio_root_none': '— 未选择 —',
+  'settings_node.audio_root_save': '保存',
+  'settings_node.audio_root_change_confirm': '更改音乐根目录会替换每位成员在“音乐”标签页中看到的内容。是否继续？',
+  'settings_node.directories_title': '目录',
+  'settings_node.directories_hint': '共享文件夹，以及“视频”和“音乐”应用各自使用哪个作为入口。',
+
   // Create group wizard
   'wizard.title': '创建群组',
   'wizard.detecting': '正在检测本地 node…',