feat(task1): restructure directories for turborepo monorepo

- Move backend/ to apps/server/ via git mv
- Move frontend/ to apps/admin/ via git mv
- Create packages/typescript-config/ with base, nestjs, and react-vite presets

packages/typescript-config/package.json

@@ -0,0 +1,7 @@
+{
+  "name": "@gongxue/typescript-config",
+  "version": "0.0.0",
+  "private": true,
+  "license": "UNLICENSED",
+  "files": ["base.json", "nestjs.json", "react-vite.json"]
+}