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/__mocks__/readability.ts

@@ -0,0 +1,6 @@
+export class Readability {
+  constructor(private doc: unknown) {}
+  parse() {
+    return { textContent: "" };
+  }
+}