feat(client): Phase 2 — per-app settings panes, folder tree, multi-directory

Each app's settings were inlined in `group-settings.js` — TMDB, MusicBrainz,
and one folder picker per app, each with its own draft state and save handler
saying the same thing about a different key. They are one file per app now,
reached through the `apps.js` registry, and the page that renders them names no
application at all: adding one is a registry entry and a settings file.

The line between the two is what makes that true. What every app has — folders
— the page does generically, through one `saveDirectories` bound to the app.
What one app alone has, its pane does itself with the transport it is handed.
An app that only needs directories touches neither `group-settings.js` nor
`group-page.js`, which is `test_app_settings_plugin.py`'s subject.

`settings-ui.js` exists because a pane importing the page that renders it is a
cycle, and ES modules answer that with a temporal-dead-zone ReferenceError at
first render — a component that silently does not appear, the fault already
recorded in CLAUDE.md about hook ordering.

The flat depth-indented `<select>` of every folder in the library becomes a
modal tree. It asks the node for nothing: the tree is derived from paths the
client already holds, so it shows exactly what the group's index contains and
adds no folder-browsing protocol. For Chat's attachment folder — the one
directory that is written to rather than read — read-only roots are greyed
out, so the node's refusal arrives before the operator picks rather than when
somebody sends a file.

Videos and Music take a list of folders. A library on two drives could not be
described before; the only recourse was pointing the app at a parent containing
both, which pulls in everything else under it. The scalar shapes survive on the
wire alone, for a node speaking MNP 1.0, and the client reads them as a
one-element list.

Two things the tests caught that I would not have:

`test_asset_versioning` — six new modules were missing from `_ASSETS`. Reached
through the registry rather than imported by name, they are exactly the files
nothing else would notice changing, and a stale one is served from cache with
no version bump.

And `node --check foo.js` does **not** reliably report a module syntax error:
it accepted `${/* ... */''}` — htm template syntax pasted into a plain object
literal — and reported success. A `.mjs` copy forces the module parser and
reports it. The suite had no syntax check at all, which is how that reached a
file; `test_spa_syntax.py` does it for every module now, and pins that the
loose path is not what it uses.

Suite: 12 failures, all pre-existing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011pvMdvLBG92jyhvD5pD6us

1 files changed, 13 insertions, 9 deletions

diff --git a/packages/meshbay-hub/src/meshbay_hub/static/music-app.js b/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
index 212745a..f622b5d 100644
--- a/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
+++ b/packages/meshbay-hub/src/meshbay_hub/static/music-app.js
@@ -52,19 +52,20 @@ function foldKey(s) {
 // tag/cover enrichment for this group before a root is chosen either,
 // daemon.py's _enrich_new_audio_entries), not "the whole shared tree" —
 // falling back to that would just show files nothing has enriched.
-function underAudioRoot(entry, audioRoot) {
-  if (!audioRoot) return false;
+function underAudioRoot(entry, directories) {
+  const dirs = directories || [];
+  if (!dirs.length) return false;
   const p = entry.path || '';
-  return p === audioRoot || p.startsWith(audioRoot + '/');
+  return dirs.some((d) => p === d || p.startsWith(d + '/'));
 }
 
-function groupMusicEntries(entries, audioRoot) {
+function groupMusicEntries(entries, musicDirectories) {
   const tracks = []; // no artist at all, even after the folder fallback -- rare, but real
   const byArtistKey = new Map(); // foldKey(artist) -> { artist, albumsByKey: Map, loose: [] }
 
   for (const e of entries) {
     if (e.type !== 'audio') continue;
-    if (!underAudioRoot(e, audioRoot)) continue;
+    if (!underAudioRoot(e, musicDirectories)) continue;
     const artistRaw = (e.artist || '').trim();
     if (!artistRaw) { tracks.push(e); continue; }
     const artistKey = foldKey(artistRaw);
@@ -453,7 +454,8 @@ function FlatList({ tracks, artists, onPlayQueue }) {
 // -- shell --------------------------------------------------------------------
 
 function MusicApp({
-  groupId, transportRef, gekRef, status, entries, availableEntries, audioRoot, musicbrainzConfig, onPlayQueue,
+  groupId, transportRef, gekRef, status, entries, availableEntries,
+  musicDirectories, musicbrainzConfig, onPlayQueue,
   hideFilter,
 }) {
   const [mode, setMode] = useState(loadViewMode);
@@ -466,8 +468,10 @@ function MusicApp({
   const setModeAndSave = (m) => { setMode(m); saveViewMode(m); };
 
   const musicEntries = availableEntries || entries;
+  const configured = (musicDirectories || []).length > 0;
   const { tracks, artists, albums } = useMemo(
-    () => groupMusicEntries(musicEntries, audioRoot), [musicEntries, audioRoot]);
+    () => groupMusicEntries(musicEntries, musicDirectories),
+    [musicEntries, musicDirectories]);
 
   const needle = filter.trim().toLowerCase();
   const filteredArtists = useMemo(() => {
@@ -493,10 +497,10 @@ function MusicApp({
     ${status === 'offline' && html`
       <p class="page-message">${t('group.offline_title')} ${t('group.offline_hint')}</p>
     `}
-    ${status === 'connected' && !audioRoot && html`
+    ${status === 'connected' && !configured && html`
       <p class="page-message">${t('music.no_root_configured')}</p>
     `}
-    ${status === 'connected' && audioRoot && html`
+    ${status === 'connected' && configured && html`
       <div class="video-toolbar">
         <button class="tb-btn ${mode === 'grid' ? 'active' : ''}"
           onClick=${() => setModeAndSave('grid')}>