feat(settings): 新增独立设置页并统一桌面偏好读取

新增 /settings 页面，集中管理桌面行为与启动偏好开关

抽离 desktop-settings 工具，统一本地布尔配置读写

首页默认跳转逻辑改为复用设置工具，减少重复实现

frontend/utils/desktop-settings.js

@@ -0,0 +1,20 @@
+export const DESKTOP_SETTING_AUTO_REALTIME_KEY = 'desktop.settings.autoRealtime'
+export const DESKTOP_SETTING_DEFAULT_TO_CHAT_KEY = 'desktop.settings.defaultToChatWhenData'
+
+export const readLocalBoolSetting = (key, fallback = false) => {
+  if (!process.client) return !!fallback
+  try {
+    const raw = localStorage.getItem(String(key || ''))
+    if (raw == null) return !!fallback
+    return String(raw).toLowerCase() === 'true'
+  } catch {
+    return !!fallback
+  }
+}
+
+export const writeLocalBoolSetting = (key, value) => {
+  if (!process.client) return
+  try {
+    localStorage.setItem(String(key || ''), value ? 'true' : 'false')
+  } catch {}
+}