refactor: restructure project into 5 core modules

Organize project by 5 core modules based on requirement docs.

Co-authored-by: null <4804959+fnvtk@users.noreply.github.com>

app/api/auth/send-code/route.ts

@@ -1,31 +0,0 @@
-import { NextRequest, NextResponse } from "next/server"
-
-/**
- * 本地验证码发送 API (mock)
- * 开发环境下直接返回成功，验证码可为任意4位以上
- */
-export async function POST(request: NextRequest) {
-  try {
-    const formData = await request.formData()
-    const phone = (formData.get("phone") || "").toString().trim()
-
-    if (!phone) {
-      return NextResponse.json(
-        { code: 40001, message: "请输入手机号" },
-        { status: 200 }
-      )
-    }
-
-    // Mock: 模拟发送成功，开发时可用 123456 等作为验证码
-    return NextResponse.json({
-      code: 10000,
-      message: "验证码已发送（开发模式：可使用任意4位以上数字）",
-    })
-  } catch (error) {
-    console.error("[auth/send-code]", error)
-    return NextResponse.json(
-      { code: 50000, message: "服务器错误" },
-      { status: 500 }
-    )
-  }
-}