refactor: 架构整固——分层单向化、全量 TypeScript、直接运行

- 移除 bd/mg 两平台及磁盘残留产物；清理 api-test 死脚本、musicSdk/message+options 死模块、infSign vendor
- musicSdk/ 改名 sdk/；src/common、src/auth、src/apis 整体移入 sdk/，依赖方向定为 src → sdk 严格单向
- src/ 手写 JS 全量转 .ts，删除 JS 类型垫片 modules.d.ts；源码 import 统一 .ts 后缀
- Node 原生类型剥离直接运行 .ts（engines >=22.18），取消 tsc 发射产物，tsc 仅类型检查（pnpm typecheck）
- 删除 kwdes 备用实现与 src/index.ts 转发垫片；测试移至 test/smoke-test.ts
- common/request.ts 补显式导出类型；修复 set-cookie 单值形态、ApiError 类字段等隐患

验证：tsc 零错误，smoke-test 41/41

package.json

@@ -3,12 +3,12 @@
   "version": "1.0.0",
   "description": "多平台音乐聚合服务器",
   "type": "module",
-  "main": "src/index.js",
+  "main": "sdk/index.ts",
   "packageManager": "pnpm@12.4.1",
   "scripts": {
-    "build": "tsc",
-    "start": "pnpm run build && node src/server.js",
-    "test": "pnpm run build && node src/smoke-test.js"
+    "typecheck": "tsc",
+    "start": "node src/server.ts",
+    "test": "pnpm run typecheck && node test/smoke-test.ts"
   },
   "dependencies": {
     "@fastify/cors": "^11.3.0",
@@ -25,5 +25,8 @@
     "@types/node": "^26.4.0",
     "playwright": "^1.62.1",
     "typescript": "^7.0.2"
+  },
+  "engines": {
+    "node": ">=22.18"
   }
 }