feat: 足迹 Footprints 个人留痕系统

桌面应用(Tauri+React+SQLite)：时间线/记录/学年学科成绩梯度/统计/类型与字段模板/附件内容寻址/详情视图/PWA

同步服务端(sync-server)：多用户+邀请码/LWW推拉/seq游标/附件去重/Docker部署

多端同步地基：uuid v7/HLC混合逻辑时钟/软删除墓碑/sync_oplog，Node与Rust双端一致并通过自动化测试

app/src/components/layout/AppShell.tsx

@@ -0,0 +1,26 @@
+import { useState } from 'react';
+import { Outlet } from 'react-router-dom';
+import { Sidebar } from './Sidebar';
+import { Header } from './Header';
+import { ToastProvider } from '@/components/ui';
+
+export function AppShell() {
+  const [navOpen, setNavOpen] = useState(false);
+
+  return (
+    <ToastProvider>
+      <div className="flex h-full">
+        {navOpen && (
+          <div className="fixed inset-0 z-30 bg-black/45 lg:hidden" onClick={() => setNavOpen(false)} aria-hidden />
+        )}
+        <Sidebar open={navOpen} onClose={() => setNavOpen(false)} />
+        <div className="flex min-w-0 flex-1 flex-col">
+          <Header onMenu={() => setNavOpen(true)} />
+          <main className="min-h-0 flex-1 overflow-y-auto">
+            <Outlet />
+          </main>
+        </div>
+      </div>
+    </ToastProvider>
+  );
+}