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/prefs-shared.ts

@@ -60,6 +60,14 @@ export interface SidebarPrefs {
    * own enable switch gates it too (both must be on for the takeover).
    */
   interceptOpenPath: boolean
+  /**
+   * Position compatibility mode: reserves space at the top for the native
+   * Windows title bar (drawn at the window's top-right corner over the web
+   * content in frameless/hidden-title-bar windows). When on, the toggle
+   * cluster drops below the strip and the right panel's content starts
+   * below it. Off by default — the sidebar layout is untouched.
+   */
+  titleBarCompat: boolean
   /**
    * Whether the HTML previewer drops its sandboxed iframe. Sandbox ON (the
    * default) renders previewed HTML in an opaque-origin iframe that cannot
@@ -159,6 +167,7 @@ export const SIDEBAR_PREFS_DEFAULTS: SidebarPrefs = {
   terminalFontFamily: '',
   terminalFontSize: TERMINAL_FONT_SIZE_DEFAULT,
   interceptOpenPath: true,
+  titleBarCompat: false,
   htmlViewerNoSandbox: false,
   htmlViewerDefaultUnsafe: false,
   browserNoSandbox: false,