Refactor Alembic setup and add migration helper script.

Updated Alembic configuration and folder structure to reference the `app` module. Introduced a new `migrate.py` script to manage migrations efficiently with commands for generating, applying, and inspecting migrations. Adjusted `env.py` to ensure proper model imports and use environment-driven database URLs.

backend/app/main.py

@@ -2,7 +2,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import HTMLResponse
 
-from app.config import settings
+from app.core.config import settings
 
 import logging