fix: 修复新版前端夜间模式

frontend/src/composables/theme.ts

@@ -0,0 +1,40 @@
+import { ref } from 'vue';
+
+export type AppTheme = 'light' | 'dark';
+
+const THEME_KEY = 'theme';
+
+export const themeName = ref<AppTheme>(readStoredTheme());
+
+applyTheme(themeName.value);
+
+export function setAppTheme(nextTheme: AppTheme) {
+  themeName.value = nextTheme;
+  applyTheme(nextTheme);
+}
+
+export function toggleAppTheme() {
+  setAppTheme(themeName.value === 'dark' ? 'light' : 'dark');
+}
+
+function readStoredTheme(): AppTheme {
+  try {
+    const stored = typeof localStorage === 'undefined' ? null : localStorage.getItem(THEME_KEY);
+    return stored === 'dark' ? 'dark' : 'light';
+  } catch {
+    return 'light';
+  }
+}
+
+function applyTheme(nextTheme: AppTheme) {
+  if (typeof document !== 'undefined') {
+    document.documentElement.setAttribute('data-theme', nextTheme);
+  }
+  try {
+    if (typeof localStorage !== 'undefined') {
+      localStorage.setItem(THEME_KEY, nextTheme);
+    }
+  } catch {
+    // Ignore storage failures so theme switching never blocks the UI.
+  }
+}