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/src/types/api.d.ts

@@ -0,0 +1,7 @@
+declare namespace API {
+    interface ErrorResponse {
+        detail: string;
+    }
+
+    // Add more types as you develop your API
+}