use node: prefix for requires

mostly because code is being autogenerated by all the AI stuff using
this prefix. it's also used in the stack trace.

src/system.js

@@ -18,7 +18,7 @@ exports = module.exports = {
 };
 
 const apps = require('./apps.js'),
-    assert = require('assert'),
+    assert = require('node:assert'),
     { AsyncTask } = require('./asynctask.js'),
     backupTargets = require('./backuptargets.js'),
     BoxError = require('./boxerror.js'),
@@ -26,11 +26,11 @@ const apps = require('./apps.js'),
     df = require('./df.js'),
     docker = require('./docker.js'),
     eventlog = require('./eventlog.js'),
-    fs = require('fs'),
+    fs = require('node:fs'),
     logs = require('./logs.js'),
     notifications = require('./notifications.js'),
-    os = require('os'),
-    path = require('path'),
+    os = require('node:os'),
+    path = require('node:path'),
     paths = require('./paths.js'),
     safe = require('safetydance'),
     shell = require('./shell.js')('system'),