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>
   )

modern/frontend/src/Integrations.jsx

@@ -30,6 +30,14 @@ export default function Integrations(){
       .finally(()=>setLoadingId(null))
   }
 
+  function previewEvents(integrationId){
+    fetch(`/api/v1/integrations/${integrationId}/events_preview`, {credentials:'include'})
+      .then(r=>r.json()).then(d=>{
+        setEvents(d)
+        setMsg('Preview loaded')
+      }).catch(()=>setMsg('Preview failed'))
+  }
+
   function removeIntegration(integrationId){
     if(!confirm('Remove integration?')) return
     setLoadingId(integrationId)
@@ -63,6 +71,7 @@ export default function Integrations(){
             <strong>{i.provider}</strong> — id: {i.id} — user: {i.user_id}
             <div style={{display:'inline-block', marginLeft:12}}>
               <button onClick={()=>fetchEvents(i.id)} disabled={loadingId===i.id} style={{marginRight:6}}>Fetch Events</button>
+              <button onClick={()=>previewEvents(i.id)} disabled={loadingId===i.id} style={{marginRight:6}}>Preview</button>
               <button onClick={()=>syncIntegration(i.id)} disabled={loadingId===i.id} style={{marginRight:6}}>Sync → Habits</button>
               <button onClick={()=>removeIntegration(i.id)} disabled={loadingId===i.id}>Remove</button>
             </div>

modern/frontend/src/Login.jsx

@@ -0,0 +1,25 @@
+import React, {useState} from 'react'
+
+export default function Login(){
+  const [email,setEmail]=useState('')
+  const [pw,setPw]=useState('')
+  const [msg,setMsg]=useState(null)
+
+  function submit(e){
+    e.preventDefault()
+    fetch('/api/v1/auth/login', {method:'POST', headers:{'Content-Type':'application/json'}, body: JSON.stringify({email, password: pw}), credentials:'include'})
+      .then(r=>r.json()).then(()=> setMsg('Logged in')).catch(()=> setMsg('Login failed'))
+  }
+
+  return (
+    <div style={{marginTop:20}}>
+      <h2>Login</h2>
+      <form onSubmit={submit}>
+        <div><input placeholder="email" value={email} onChange={e=>setEmail(e.target.value)} /></div>
+        <div><input placeholder="password" type="password" value={pw} onChange={e=>setPw(e.target.value)} /></div>
+        <button type="submit">Login</button>
+      </form>
+      {msg && <div style={{marginTop:8}}>{msg}</div>}
+    </div>
+  )
+}