auth: add JWT email/password auth + Login UI; security: kms rotate helper; preview sync endpoint + UI

modern/frontend/src/App.jsx

@@ -1,13 +1,15 @@
 import React from 'react'
 import Integrations from './Integrations'
 import Guilds from './Guilds'
+import Login from './Login'
 
 export default function App(){
   return (
     <div style={{padding:20,fontFamily:'system-ui, sans-serif'}}>
       <h1>LifeRPG Modern</h1>
       <p>Welcome — frontend scaffold. Connect to backend at <code>/api/v1</code>.</p>
-      <Integrations />
+  <Login />
+  <Integrations />
   <Guilds />
     </div>
   )