feat(web): 添加响应式布局和 PWA 支持

- 实现移动端响应式适配：抽屉式侧边栏、触摸优化、Safe Area 支持
- 添加 PWA 支持：vite-plugin-pwa、manifest、Service Worker 缓存
- 优化移动端输入体验：防缩放、最小触摸目标、键盘适配

packages/web/public/manifest.json

@@ -0,0 +1,19 @@
+{
+  "name": "AI Terminal Assistant",
+  "short_name": "AI Assistant",
+  "description": "Your intelligent coding companion",
+  "theme_color": "#111827",
+  "background_color": "#111827",
+  "display": "standalone",
+  "orientation": "portrait-primary",
+  "scope": "/",
+  "start_url": "/",
+  "icons": [
+    {
+      "src": "/icon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}