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/admin

@@ -0,0 +1,37 @@
+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()
+
+# DELETE ITEM
+@app.delete("/items/{item_id}")
+def delete_item(
+    item_id: int,
+    db: Session = Depends(get_db)
+):
+    item = crud.delete_item(db, item_id)
+
+    if not item:
+        raise HTTPException(
+            status_code=404,
+            detail="Item not found"
+        )
+
+    return {"message": "Item deleted"}
+
+    # CREATE ITEM
+@app.post("/items", response_model=schemas.ItemResponse)
+def create_item(
+    item: schemas.ItemCreate,
+    db: Session = Depends(get_db)
+):
+    return crud.create_item(db, item.title)