feat(backend): add SIMPLE_STREAMING WebRTC control-path streaming

Backend/routes/commands.ts

@@ -4,6 +4,7 @@ import { z } from 'zod';
 
 import { db } from '../db/client';
 import { deviceCommands, deviceLinks, devices } from '../db/schema';
+import { simpleStreamingEnabled } from '../media/config';
 import { requireAuth } from '../middleware/auth';
 import { requireDeviceAuth } from '../middleware/device-auth';
 import { dispatchCommandById } from '../realtime/gateway';
@@ -47,6 +48,13 @@ router.post('/', requireAuth, async (req, res) => {
     return;
   }
 
+  if (simpleStreamingEnabled && parsed.data.commandType === 'start_stream') {
+    res.status(409).json({
+      message: 'start_stream commands are disabled while SIMPLE_STREAMING is enabled; use /streams/request instead',
+    });
+    return;
+  }
+
   if (parsed.data.sourceDeviceId === parsed.data.targetDeviceId) {
     res.status(400).json({ message: 'sourceDeviceId and targetDeviceId must differ' });
     return;