refactor: integrate Alembic, restructure project, and clean up

- Add Alembic configuration (alembic.ini, env.py) for database migrations
- Remove legacy wheel.db and unnecessary __pycache__ files
- Delete models.py to separate SQLAlchemy and Pydantic concerns
- Restructure main.py to use modular API routers (user/admin)
- Introduce config backend for centralized settings management

backend/api/user

@@ -0,0 +1,38 @@
+from fastapi import FastAPI, Depends, HTTPException
+from sqlalchemy.orm import Session
+from fastapi.middleware.cors import CORSMiddleware
+
+import models
+import schemas
+import crud
+
+from database import SessionLocal, engine
+
+models.Base.metadata.create_all(bind=engine)
+
+app = FastAPI()
+
+
+# SPIN
+@app.post("/spin")
+def spin(db: Session = Depends(get_db)):
+
+    winner = crud.spin_wheel(db)
+
+    if not winner:
+        raise HTTPException(
+            status_code=400,
+            detail="No items available"
+        )
+
+    return {
+        "winner": {
+            "id": winner.id,
+            "title": winner.title
+        }
+    }
+
+   # GET ITEMS
+@app.get("/items", response_model=list[schemas.ItemResponse])
+def get_items(db: Session = Depends(get_db)):
+    return crud.get_items(db)