Fix backend message forwarding to use proper JSON encoding instead of string formatting

vidai/backend.py

@@ -61,7 +61,13 @@ def handle_web_message(message: Message, client_sock=None) -> Message:
             print(f"DEBUG: Backend forwarding analyze_request {message.msg_id} to worker {worker_key}")
         if worker_key in worker_sockets:
             # Forward to local worker
-            msg_json = f'{{"msg_type": "{message.msg_type}", "msg_id": "{message.msg_id}", "data": {message.data}}}\n'
+            import json
+            msg_dict = {
+                'msg_type': message.msg_type,
+                'msg_id': message.msg_id,
+                'data': message.data
+            }
+            msg_json = json.dumps(msg_dict) + '\n'
             if get_debug():
                 print(f"DEBUG: Sending to worker: {msg_json.strip()}")
             worker_sockets[worker_key].sendall(msg_json.encode('utf-8'))