style(appShell): 优化应用外壳及底部导航样式与结构

- 在 tailwind 配置中添加应用外壳相关的 safelist 类名
- 替换 App.tsx 中应用外壳容器的类名，去除多余的内边距容器
- 在现代和遗留样式文件中新增移动端全屏、桌面居中列的样式规则
- 新增底部导航外层和内层的样式及响应式布局支持
- appShell.ts 中将样式类改为统一的 x8- 前缀类名
- BottomNav 组件使用新的样式类名以匹配样式调整
- Home 页面 ListRow 组件支持可选缩略图展示，增加界面展示丰富度

client/src/lib/appShell.ts

@@ -1,8 +1,8 @@
 /** Centered phone-style shell width (desktop / ultrawide). */
 export const APP_SHELL_MAX_PX = 1180;
 
-/** Inner column inside horizontal gutters — use with a flex/grid centering parent. */
-export const appShellColumnClass =
-  "w-full min-w-0 max-w-[min(1180px,100%)]";
-
-export const appShellGutterClass = "px-4 sm:px-6";
+/** Responsive rules live in `.x8-app-shell-*` (index.css + index.legacy.css). */
+export const appShellOuterClass = "x8-app-shell-outer";
+export const appShellColumnClass = "x8-app-shell-column";
+export const bottomNavOuterClass = "x8-bottom-nav-outer";
+export const bottomNavInnerClass = "x8-bottom-nav-inner";