feat: phone login via QR when the saved Mudfish login expires

When autologin is rejected the panel offers '휴대폰으로 로그인 (QR)'. It opens
a 5-minute LAN relay to the launcher UI guarded by a one-time token (first
phone to open the QR URL is the only client allowed) and shows the URL as a
QR code. The relay closes as soon as a new session appears, on cancel, on
expiry, and on unload.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/Panel.tsx

@@ -4,8 +4,10 @@ import {
   Field,
   PanelSection,
   PanelSectionRow,
+  showModal,
   ToggleField,
 } from "@decky/ui";
+import { LoginModal } from "./LoginModal";
 import { useEffect, useRef, useState } from "react";
 import {
   connect,
@@ -158,6 +160,13 @@ export function Panel() {
           <Field focusable={false} description={state.message} />
         </PanelSectionRow>
       )}
+      {state.need_login && (
+        <PanelSectionRow>
+          <ButtonItem layout="below" onClick={() => showModal(<LoginModal />)}>
+            휴대폰으로 로그인 (QR)
+          </ButtonItem>
+        </PanelSectionRow>
+      )}
       <PanelSectionRow>
         <ButtonItem layout="below" onClick={() => setAdvanced(!advanced)}>
           {advanced ? "고급 ▾" : "고급 ▸"}