Remove build-time Mongo caching since HF blocks it, rely on runtime startup

Pre-download MongoDB memory server binary during Docker build step to fix HF startup timeouts

Change Docker base image to full node:22 to include libcurl for MongoDB memory server

Change Docker base image to node:22-slim to support mongodb-memory-server

Update Node.js version to 22 for Vite 8 compatibility

Deploy full stack frontend and backend together