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/base.json

@@ -0,0 +1,8 @@
+{
+  "compilerOptions": {
+    "target": "ES2023",
+    "skipLibCheck": true,
+    "strictNullChecks": true,
+    "forceConsistentCasingInFileNames": true
+  }
+}