moh: music-on-hold classes, uploads, pickers for users and queues

/api/moh-classes: create (slug, not "default"), delete (409 while an
extension or queue uses it), add/play/remove files. Files are 8 kHz
wav in MOH_DIR/<class>/ and sound_files rows of kind moh. Extensions
and queues may only pick default or an existing class.

Two things found with real calls, written back into 03 and 04:
- An empty class plays silence on Asterisk 24. Only classes with
  music are rendered, so a channel asking for an empty one gets
  default.
- The generator reloads only changed files, and a file upload changes
  no config (except a class's first/last). The route sends moh reload
  after every file change.

Web: a Music on hold section on Sounds & music, and a select of sets
in the user drawer's Phone tab and the queue form. load-golden makes
the class folders like the api does. Golden case queue gains two
classes. e2e m8-t5: set made in the UI, upload listed by Asterisk, a
queue caller hears it, a user's moh_suggest, delete refused while
used, an emptied set falls back to default.

Task: M8-T5

apps/api/src/generator/index.ts

@@ -20,6 +20,7 @@ import { renderEmergency } from './dialplan/emergency.ts';
 import { renderRingGroups } from './dialplan/ringgroups.ts';
 import { renderQueueDialplan } from './dialplan/queues.ts';
 import { renderQueues } from './queues.ts';
+import { renderMoh } from './moh.ts';
 import { renderConfbridge, renderConferences } from './dialplan/conferences.ts';
 import { renderPaging } from './dialplan/paging.ts';
 import { renderIvrs } from './dialplan/ivrs.ts';
@@ -51,6 +52,7 @@ export type RenderedFiles = Record<GeneratedFileName, string>;
 const BODIES: Partial<Record<GeneratedFileName, (snap: Snapshot) => string>> = {
   'pjsip_selfphoneng.conf': renderPjsip,
   'rtp_selfphoneng.conf': renderRtp,
+  'musiconhold_selfphoneng.conf': renderMoh,
   'extensions_globals_selfphoneng.conf': renderGlobals,
   'voicemail_selfphoneng.conf': renderVoicemail,
   'queues_selfphoneng.conf': renderQueues,