feat: add AI summary / transcript integration for recordings

Ported from greenlight-tm: when TRANSCRIPTION_API_URL and
TRANSCRIPTION_API_KEY are set in the .env and the per-room
"AI summary / transcript" setting is enabled, Redlight POSTs to
${TRANSCRIPTION_API_URL}/prompt (header X-Api-Key) as soon as the
"video" format of a recording becomes available.

- transcription.js: service with env gating, timeout and logging
- bbb.js: pass meta_bbb-recording-ready-url on meeting create when the
  room has the setting enabled
- recordings.js: unauthenticated /recording-ready callback that
  verifies BBB's signed_parameters JWT (HS256, shared secret), caches
  the recording and requests the transcription once per recording
  (deduped via transcript_requested_at)
- rooms: new recording_transcript column, accepted on create/update
- branding endpoint exposes transcriptionEnabled so the UI only shows
  the toggle when the server is configured
- RoomDetail: toggle under "Allow recording" (disabled when recording
  is off), de/en i18n
- chore: bump version to 2.4.0

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/config/bbb.js

@@ -2,6 +2,7 @@
 import xml2js from 'xml2js';
 import { log, fmtDuration, fmtStatus, fmtMethod, fmtReturncode, sanitizeBBBParams } from './logger.js';
 import { t } from './emaili18n.js';
+import { isTranscriptionEnabled } from './transcription.js';
 
 const BBB_URL = process.env.BBB_URL || 'https://your-bbb-server.com/bigbluebutton/api/';
 const BBB_SECRET = process.env.BBB_SECRET || '';
@@ -115,6 +116,11 @@ export async function createMeeting(room, logoutURL, loginURL = null, presentati
   if (analyticsCallbackURL) {
     params['meta_analytics-callback-url'] = analyticsCallbackURL;
   }
+  // BBB posts a signed recording-ready callback there once recording formats
+  // are processed; used to trigger the AI summary/transcript integration.
+  if (logoutURL && room.recording_transcript && isTranscriptionEnabled()) {
+    params['meta_bbb-recording-ready-url'] = `${logoutURL}/api/recordings/recording-ready`;
+  }
 
   // Build optional presentation XML body - escape URL to prevent XML injection
   let xmlBody = null;