Add Dockerized FastNext stack template with backend and frontend

Implemented a full-stack template combining Next.js (frontend), FastAPI (backend), and PostgreSQL. Included Docker configurations for development and production, environment file templates, Makefile commands, and initial setup for database migrations and builds. The stack is production-ready and supports hot-reloading for local development.

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
+}