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/routes/rooms.js

@@ -193,6 +193,7 @@ router.post('/', authenticateToken, async (req, res) => {
       record_meeting,
       guest_access,
       moderator_code,
+      recording_transcript,
     } = req.body;
 
     if (!name || name.trim().length === 0) {
@@ -227,8 +228,8 @@ router.post('/', authenticateToken, async (req, res) => {
     const db = getDb();
 
     const result = await db.run(`
-      INSERT INTO rooms (uid, name, user_id, welcome_message, max_participants, access_code, mute_on_join, require_approval, anyone_can_start, all_join_moderator, record_meeting, guest_access, moderator_code)
-      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+      INSERT INTO rooms (uid, name, user_id, welcome_message, max_participants, access_code, mute_on_join, require_approval, anyone_can_start, all_join_moderator, record_meeting, guest_access, moderator_code, recording_transcript)
+      VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
     `, [
       uid,
       name.trim(),
@@ -243,6 +244,7 @@ router.post('/', authenticateToken, async (req, res) => {
       record_meeting !== false ? 1 : 0,
       guest_access ? 1 : 0,
       moderator_code || null,
+      recording_transcript ? 1 : 0,
     ]);
 
     const room = await db.get('SELECT * FROM rooms WHERE id = ?', [result.lastInsertRowid]);
@@ -277,6 +279,7 @@ router.put('/:uid', authenticateToken, async (req, res) => {
       moderator_code,
       learning_analytics,
       analytics_visibility,
+      recording_transcript,
     } = req.body;
 
     // M12: field length limits (same as create)
@@ -318,6 +321,7 @@ router.put('/:uid', authenticateToken, async (req, res) => {
         moderator_code = ?,
         learning_analytics = COALESCE(?, learning_analytics),
         analytics_visibility = COALESCE(?, analytics_visibility),
+        recording_transcript = COALESCE(?, recording_transcript),
         updated_at = CURRENT_TIMESTAMP
       WHERE uid = ?
     `, [
@@ -334,6 +338,7 @@ router.put('/:uid', authenticateToken, async (req, res) => {
       moderator_code !== undefined ? (moderator_code || null) : room.moderator_code,
       learning_analytics !== undefined ? (learning_analytics ? 1 : 0) : null,
       analytics_visibility && ['owner', 'shared'].includes(analytics_visibility) ? analytics_visibility : null,
+      recording_transcript !== undefined ? (recording_transcript ? 1 : 0) : null,
       req.params.uid,
     ]);