Add frontend service to Docker setup and configure networking

Introduced a new `frontend` service in `docker-compose.yml`, complete with build, healthchecks, and networking. Added a multi-stage Dockerfile for the frontend, a `.dockerignore` file, and a startup script to wait for the backend. Updated Next.js configuration for Docker compatibility and added API type definitions.

frontend/entrypoint.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+# Wait for backend to be ready
+echo "Waiting for backend..."
+until nc -z backend 8000; do
+    sleep 1
+done
+echo "Backend is up!"
+
+# Start the Next.js application
+exec "$@"