Feature: Initialize FastAPI Backend Project Structure

[felixjordandev]

This PR establishes the foundational directory structure for the new FastAPI backend, including a basic health check endpoint.

Changes

• Created a backend/ root folder to house all backend-related code.
• Set up core subdirectories within backend/app/ for better organization: api/, core/, models/, services/, and utils/.
• Added an __init__.py file to backend/app/ to properly mark it as a Python package.
• Implemented a main.py file at the project root, serving as the FastAPI entry point with a simple /health check.

[klingonaston]

the /health check is a solid start for the FastAPI setup—nice structure overall!