chore(repo): restructure as monorepo with server and client workspaces

- move NestJS app into server/ subdirectory
- add client/ React+TypeScript (Vite) app with Hello World
- update docker-compose to build and run both services
- add root package.json declaring npm workspaces
- update .gitignore to cover node_modules and dist at all depths

server/test/tsconfig.json

@@ -0,0 +1,9 @@
+{
+  "extends": "../tsconfig.json",
+  "compilerOptions": {
+    "rootDir": "..",
+    "noEmit": true,
+    "types": ["jest", "node"]
+  },
+  "exclude": []
+}