fix: send literal \\n (0x5c 0x6e) delimiter — matches HttpResponseStream split('\\n')

Confirmed via xxd on bricks.js: split('\\n') splits on backslash-n literal.
Backend now yields json + '\\n', matching LmmIO streaming pattern.
Frontend: clean AgentIO with url, no ready bind.

wwwroot/index_cockpit.ui

@@ -200,14 +200,5 @@
                 }
             ]
         }
-    ],
-    "binds": [
-        {
-            "wid": "self",
-            "event": "ready",
-            "actiontype": "script",
-            "target": "self",
-            "script": "console.log('DIAG: VBox ready');var ai=bricks.getWidgetById('chat_input',bricks.app);console.log('DIAG: chat_input=',ai?'found':'NOT FOUND','type=',ai?ai.constructor.name:'N/A','url=',ai?ai.opts.url:'N/A');if(ai&&ai.inputw){ai.inputw.unbind('inputed');ai.inputw.bind('inputed',function(e){console.log('DIAG: inputed params=',JSON.stringify(e.params));});}"
-        }
     ]
 }