feat: add optional TOTP MFA for email/password accounts

- Add MFA enrollment UI in new Settings page with QR code and backup secret
- Add TOTP challenge step to login flow for enrolled users
- Check AAL after login and show TOTP input when aal2 required
- Add disable MFA option with TOTP re-verification
- Only show MFA options for email/password users (not OAuth)
- Add Settings link to user dropdown menu

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/Login.tsx

@@ -7,9 +7,11 @@ const isLocalDev = import.meta.env['VITE_SUPABASE_URL']?.includes('localhost') ?
 export function Login() {
   const [email, setEmail] = useState('')
   const [password, setPassword] = useState('')
+  const [totpCode, setTotpCode] = useState('')
   const [error, setError] = useState<string | null>(null)
   const [loading, setLoading] = useState(false)
-  const { signInWithEmail, signInWithGoogle, signInWithDiscord } = useAuth()
+  const [showMfaChallenge, setShowMfaChallenge] = useState(false)
+  const { signInWithEmail, signInWithGoogle, signInWithDiscord, verifyMfa } = useAuth()
   const navigate = useNavigate()
   const location = useLocation()
 
@@ -20,11 +22,29 @@ export function Login() {
     setError(null)
     setLoading(true)
 
-    const { error } = await signInWithEmail(email, password)
+    const { error, requiresMfa } = await signInWithEmail(email, password)
     setLoading(false)
 
     if (error) {
       setError(error.message)
+    } else if (requiresMfa) {
+      setShowMfaChallenge(true)
+    } else {
+      navigate(from, { replace: true })
+    }
+  }
+
+  async function handleMfaSubmit(e: React.FormEvent) {
+    e.preventDefault()
+    setError(null)
+    setLoading(true)
+
+    const { error } = await verifyMfa(totpCode)
+    setLoading(false)
+
+    if (error) {
+      setError(error.message)
+      setTotpCode('')
     } else {
       navigate(from, { replace: true })
     }
@@ -42,6 +62,68 @@ export function Login() {
     if (error) setError(error.message)
   }
 
+  if (showMfaChallenge) {
+    return (
+      <div className="min-h-[80vh] flex items-center justify-center px-4">
+        <div className="w-full max-w-sm space-y-6">
+          <div className="text-center">
+            <h1 className="text-2xl font-bold">Two-Factor Authentication</h1>
+            <p className="text-text-secondary mt-1">Enter the code from your authenticator app</p>
+          </div>
+
+          {error && (
+            <div className="bg-red-500/10 border border-red-500/20 text-red-400 px-4 py-3 rounded-lg text-sm">
+              {error}
+            </div>
+          )}
+
+          <form onSubmit={handleMfaSubmit} className="space-y-4">
+            <div>
+              <label
+                htmlFor="totp-code"
+                className="block text-sm font-medium text-text-secondary mb-1"
+              >
+                Authentication code
+              </label>
+              <input
+                id="totp-code"
+                type="text"
+                inputMode="numeric"
+                pattern="[0-9]*"
+                maxLength={6}
+                value={totpCode}
+                onChange={(e) => setTotpCode(e.target.value.replace(/\D/g, ''))}
+                autoFocus
+                className="w-full px-3 py-2 bg-surface-2 border border-border-default rounded-lg focus:outline-none focus:ring-2 focus:ring-accent-500 text-center text-lg tracking-widest font-mono"
+                autoComplete="one-time-code"
+              />
+            </div>
+
+            <button
+              type="submit"
+              disabled={totpCode.length !== 6 || loading}
+              className="w-full py-2 px-4 bg-accent-600 hover:bg-accent-700 disabled:opacity-50 disabled:cursor-not-allowed text-white font-medium rounded-lg transition-colors"
+            >
+              {loading ? 'Verifying...' : 'Verify'}
+            </button>
+          </form>
+
+          <button
+            type="button"
+            onClick={() => {
+              setShowMfaChallenge(false)
+              setTotpCode('')
+              setError(null)
+            }}
+            className="w-full text-center text-sm text-text-secondary hover:text-text-primary"
+          >
+            Back to login
+          </button>
+        </div>
+      </div>
+    )
+  }
+
   return (
     <div className="min-h-[80vh] flex items-center justify-center px-4">
       <div className="w-full max-w-sm space-y-6">