refactor: 标准化项目结构 frontend/ + backend/ + SQLite + run.sh

- 目录重构: app/ -> frontend/，与 backend/ 并列
- 数据库: 默认 SQLite（零配置），修复 DSN() bug
- run.sh: 一键启动前后端，支持 start/stop/restart/status
- Makefile: install/dev/build/lint/clean 快捷命令
- vite.config.ts: 配置 dev server 端口 5173 + API 代理到 8080
- config.yaml: SQLite 默认配置，开箱即用
- docs/: 完整开发文档（项目结构/API/数据库/规范/部署）
- 修复: GORM foreign key 关联声明
- 修复: go get gorm.io/driver/sqlite 依赖

frontend/src/components/ui/switch.tsx

@@ -0,0 +1,31 @@
+"use client"
+
+import * as React from "react"
+import * as SwitchPrimitive from "@radix-ui/react-switch"
+
+import { cn } from "@/lib/utils"
+
+function Switch({
+  className,
+  ...props
+}: React.ComponentProps<typeof SwitchPrimitive.Root>) {
+  return (
+    <SwitchPrimitive.Root
+      data-slot="switch"
+      className={cn(
+        "peer data-[state=checked]:bg-primary data-[state=unchecked]:bg-input focus-visible:border-ring focus-visible:ring-ring/50 dark:data-[state=unchecked]:bg-input/80 inline-flex h-[1.15rem] w-8 shrink-0 items-center rounded-full border border-transparent shadow-xs transition-all outline-none focus-visible:ring-[3px] disabled:cursor-not-allowed disabled:opacity-50",
+        className
+      )}
+      {...props}
+    >
+      <SwitchPrimitive.Thumb
+        data-slot="switch-thumb"
+        className={cn(
+          "bg-background dark:data-[state=unchecked]:bg-foreground dark:data-[state=checked]:bg-primary-foreground pointer-events-none block size-4 rounded-full ring-0 transition-transform data-[state=checked]:translate-x-[calc(100%-2px)] data-[state=unchecked]:translate-x-0"
+        )}
+      />
+    </SwitchPrimitive.Root>
+  )
+}
+
+export { Switch }