fix(web): hide login button when logged out to fix header icon alignment

未登录时 UserChip 的登录按钮使用了深色背景配色（cream-50 色系），
在首页浅色背景上不可见但仍占据约 60px 宽度，导致齿轮/GitHub/X
图标被推离右边缘。改为未登录时不渲染 UserChip，登录入口保留在
开始游戏等需要认证的操作流程中。

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

app/page.tsx

@@ -1666,7 +1666,7 @@ export default function HomePage() {
           >
             <i className="fa-brands fa-x-twitter" />
           </a>
-          <UserChip onLoginClick={() => setAuthModalOpen(true)} />
+          <UserChip />
         </div>
       </header>
 

app/play/page.tsx

@@ -2574,7 +2574,7 @@ function PlayInner() {
             <span className="text-clay-300">·</span>
             <span>{String(beatCount).padStart(3, "0")} · 拍</span>
           </div>
-          <UserChip onLoginClick={() => setAuthModalOpen(true)} />
+          <UserChip />
         </div>
       </header>
 

components/UserChip.tsx

@@ -5,11 +5,7 @@ import { AUTH_ENABLED } from "@/lib/supabase/config";
 import { createClient } from "@/lib/supabase/client";
 import type { AuthChangeEvent, Session, User } from "@supabase/supabase-js";
 
-export function UserChip({
+export function UserChip() {
-  onLoginClick,
-}: {
-  onLoginClick: () => void;
-}) {
   const [user, setUser] = useState<User | null>(null);
   const [menuOpen, setMenuOpen] = useState(false);
 
@@ -32,20 +28,7 @@ export function UserChip({
     setMenuOpen(false);
   }, []);
 
-  if (!AUTH_ENABLED) return null;
+  if (!AUTH_ENABLED || !user) return null;
-
-  if (!user) {
-    return (
-      <button
-        type="button"
-        onClick={onLoginClick}
-        className="flex items-center gap-1.5 rounded-full border border-cream-50/15 bg-cream-50/[0.06] px-3 py-1.5 text-[11px] text-cream-50/70 transition-colors hover:bg-cream-50/[0.12] hover:text-cream-50/90"
-      >
-        <i className="fa-solid fa-right-to-bracket text-[10px]" />
-        登录
-      </button>
-    );
-  }
 
   const label =
     user.user_metadata?.full_name ??