fix(web): stop QEMU serial stdin from triggering browser input prompts

web/app.js

@@ -202,6 +202,7 @@ async function boot(file, variant, setStatus) {
     mainScriptUrlOrBlob: qemuUrl.href,
     print: message => { console.log(message); logLine(message); },
     printErr: message => { console.error(message); logLine(message); },
+    stdin: () => null,
   };
   options.preRun = [() => {
     options.FS.mkdir('/bios');