feat(media): add single-server SFU scaffolding and media mode config

Backend/routes/ops.ts

@@ -1,7 +1,9 @@
 import { Router } from 'express';
 
 import { db } from '../db/client';
+import { mediaConfig } from '../media/config';
 import { mediaProvider } from '../media/service';
+import { sfuService } from '../media/sfu/service';
 import { getAllMetrics } from '../observability/metrics';
 import { minioBucket, minioClient } from '../utils/minio';
 
@@ -21,7 +23,9 @@ router.get('/ready', async (_req, res) => {
       checks: {
         database: 'ok',
         minio: 'ok',
+        mediaMode: mediaConfig.mode,
         mediaProvider: mediaProvider.name,
+        sfuService: sfuService ? sfuService.mode : 'disabled',
       },
       timestamp: new Date().toISOString(),
     });