refactor: 迁移前端到 React 19 + Zustand + Tailwind CSS v4

- 将 vanilla TS 单文件 (app.ts 395行) 拆分为 React 组件化架构
- 引入 Zustand 管理全局状态 (连接/录音/预览/历史/toast)
- 自定义 hooks 封装 WebSocket 连接和音频录制管线
- CSS 全面 Tailwind 化，style.css 从 234 行精简到 114 行 (仅保留 tokens + keyframes)
- 新增依赖: react, react-dom, zustand, @vitejs/plugin-react
- Go 后端 embed 路径 web/dist 不变，无需改动

web/package.json

@@ -12,8 +12,16 @@
 	"devDependencies": {
 		"@biomejs/biome": "^2.4.4",
 		"@tailwindcss/vite": "^4.2.1",
+		"@types/react": "^19.2.14",
+		"@types/react-dom": "^19.2.3",
+		"@vitejs/plugin-react": "^5.1.4",
 		"tailwindcss": "^4.2.1",
 		"typescript": "^5.9.3",
 		"vite": "^7.3.1"
+	},
+	"dependencies": {
+		"react": "^19.2.4",
+		"react-dom": "^19.2.4",
+		"zustand": "^5.0.11"
 	}
 }