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, 20 insertions, 0 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/transport.js b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
index 4f8e3b5..817db7a 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/transport.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/transport.js
@@ -109,6 +109,7 @@ class MeshBayTransport {
   set onTmdbConfig(fn) { this._onTmdbConfig = fn; }
   set onTmdbEnabled(fn) { this._onTmdbEnabled = fn; }
   set onVideoRoot(fn) { this._onVideoRoot = fn; }
+  set onAudioRoot(fn) { this._onAudioRoot = fn; }
   set onMusicbrainzConfig(fn) { this._onMusicbrainzConfig = fn; }
   set onMusicbrainzEnabled(fn) { this._onMusicbrainzEnabled = fn; }
   set onIndexProgress(fn) { this._onIndexProgress = fn; }
@@ -606,6 +607,19 @@ class MeshBayTransport {
   }
 
   /**
+   * Same shape as setVideoRoot above — the Music app's own entry point.
+   */
+  async setAudioRoot(path, signFn) {
+    const clean = (path || '').replace(/^\/+|\/+$/g, '');
+    const msg = await this._sendAndWait({ type: 'audio_root', v: '0.10', path: clean });
+    if (msg.type === 'error') throw new Error(msg.detail);
+    if (msg.type === 'admin_challenge') {
+      return this._authorizeAdminOp(msg, 'audio_root', clean, signFn);
+    }
+    return msg;
+  }
+
+  /**
    * MusicBrainz metadata for one track's path (Music app, docs/musicbay.md
    * §4.3) — same shape as fetchMediaMeta, minus a season/episode concept:
    * album-level (release), resolved from the track's own artist/album
@@ -1540,6 +1554,12 @@ class MeshBayTransport {
       this._onVideoRoot(msg.path || '');
     }
 
+    // Same shape: the operator changed which folder is the Music app's
+    // entry point for this group.
+    if (msg.type === 'audio_root_ack' && this._onAudioRoot) {
+      this._onAudioRoot(msg.path || '');
+    }
+
     // Node-wide, like tmdb_config_ack above — no token equivalent to hide,
     // only whether a contact string is configured (docs/musicbay.md §3.2).
     if (msg.type === 'musicbrainz_config_ack' && this._onMusicbrainzConfig) {