refactor: 将退出登录功能从顶部导航栏移至设置面板

frontend/src/App.css

@@ -1710,34 +1710,23 @@ body {
   color: var(--color-primary-hover);
 }
 
-/* ---- User badge in header ---- */
+/* ---- Logout button in config panel ---- */
 
-.header__user {
-  display: flex;
-  align-items: center;
-  gap: 8px;
-  font-size: 0.78rem;
-  color: var(--color-text-muted);
-}
-
-.header__username {
-  font-weight: 500;
-  color: var(--color-text);
-}
-
-.header__logout-btn {
-  background: none;
-  border: 1px solid var(--color-border);
-  color: var(--color-text-muted);
-  font-size: 0.72rem;
-  font-weight: 500;
-  padding: 4px 10px;
+.config-logout-btn {
+  width: 100%;
+  margin-top: 12px;
+  padding: 9px 0;
+  border: 1px solid rgba(248, 113, 113, 0.25);
   border-radius: var(--radius-sm);
+  background: rgba(248, 113, 113, 0.08);
+  color: var(--color-error);
+  font-size: 0.82rem;
+  font-weight: 600;
   cursor: pointer;
   transition: all var(--transition-fast);
 }
 
-.header__logout-btn:hover {
-  border-color: var(--color-error);
-  color: var(--color-error);
+.config-logout-btn:hover {
+  background: rgba(248, 113, 113, 0.15);
+  border-color: rgba(248, 113, 113, 0.4);
 }