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/database.js

@@ -879,6 +879,18 @@ export async function initDatabase() {
     `);
   }
 
+  // ── Recording transcription / AI summary ────────────────────────────────
+  if (!(await db.columnExists('rooms', 'recording_transcript'))) {
+    await db.exec('ALTER TABLE rooms ADD COLUMN recording_transcript INTEGER DEFAULT 0');
+  }
+  if (!(await db.columnExists('recordings', 'transcript_requested_at'))) {
+    if (isPostgres) {
+      await db.exec('ALTER TABLE recordings ADD COLUMN transcript_requested_at TIMESTAMP DEFAULT NULL');
+    } else {
+      await db.exec('ALTER TABLE recordings ADD COLUMN transcript_requested_at DATETIME DEFAULT NULL');
+    }
+  }
+
   // ── Default admin (only on very first start) ────────────────────────────
   const adminAlreadySeeded = await db.get("SELECT value FROM settings WHERE key = 'admin_seeded'");
   if (!adminAlreadySeeded) {