feat: 侧边栏新增位置兼容模式，为 Windows 原生标题栏预留顶部空间

新增 SidebarPrefs.titleBarCompat 设置项（默认关闭）：开启后 toggle cluster
下移 40px、右侧面板内容从标题栏条带下方开始，避免被 Windows 无边框窗口
右上角的原生标题栏遮挡。底部面板不受影响。设置页「常规」新增一行开关，
zh/en 双语，读写下穿既有 settings 路由。测试覆盖 parsePrefs 回退、schema
默认值、设置页渲染与开关状态。

src/client/locales.ts

@@ -116,6 +116,8 @@ export const zh = {
   settingsWidthSuffix: '%',
   settingsOpenPathTitle: '聊天区文件在侧边栏打开',
   settingsOpenPathDesc: '在聊天里点击文件链接（工具行、产物列表、文件提及）时，在侧边栏编辑器中打开，不再调用系统默认应用',
+  settingsTitleBarTitle: '位置兼容模式',
+  settingsTitleBarDesc: '为 Windows 右上角的原生标题栏预留空间：侧边栏按钮与侧边栏内容整体下移，避免被标题栏遮挡',
   settingsSaveFailed: '保存失败',
   settingsConflict: '设置已被其他窗口修改，请重试',
   binaryNoPreview: '此文件类型不支持预览',
@@ -333,6 +335,8 @@ export const en: Record<keyof typeof zh, string> = {
   settingsWidthSuffix: '%',
   settingsOpenPathTitle: 'Open chat files in the sidebar',
   settingsOpenPathDesc: 'Open file links in the chat (tool rows, produced files, mentions) in the sidebar editor instead of the system default app',
+  settingsTitleBarTitle: 'Position compatibility mode',
+  settingsTitleBarDesc: 'Reserve space for the native Windows title bar at the top-right so the sidebar buttons and content sit below it instead of underneath',
   settingsSaveFailed: 'Failed to save',
   settingsConflict: 'The setting changed in another window — please retry',
   binaryNoPreview: 'This file type cannot be previewed',