Add display_name support for users in backend and frontend

This commit introduces the `display_name` field to the user model. It updates database migrations, API endpoints, and the admin panel to handle this field. Additionally, the `display_name` is now shown in the TopBar and WinnerBadge components, improving user experience.

backend/app/routes/admin.py

@@ -19,21 +19,53 @@ def require_admin(req: Request, db: Session) -> User:
 def list_users(req: Request, db: Session = Depends(get_db)):
     require_admin(req, db)
     users = db.query(User).order_by(User.created_at.desc()).all()
-    return [{"id": u.id, "email": u.email, "role": u.role, "disabled": u.disabled} for u in users]
+    return [
+        {
+            "id": u.id,
+            "email": u.email,
+            "display_name": u.display_name,
+            "role": u.role,
+            "disabled": u.disabled,
+        }
+        for u in users
+    ]
 
 @router.post("/users")
 def create_user(req: Request, data: dict, db: Session = Depends(get_db)):
     require_admin(req, db)
     email = (data.get("email") or "").lower().strip()
     password = data.get("password") or ""
+    display_name = (data.get("display_name") or "").strip()
+
     if not email or not password:
         raise HTTPException(400, "email/password required")
     if db.query(User).filter(User.email == email).first():
         raise HTTPException(409, "email exists")
+
     role = data.get("role") or Role.user.value
     if role not in (Role.admin.value, Role.user.value):
         raise HTTPException(400, "invalid role")
-    u = User(email=email, password_hash=hash_password(password), role=role)
+
+    u = User(email=email, password_hash=hash_password(password), role=role, display_name=display_name)
     db.add(u); db.commit()
     return {"ok": True, "id": u.id}
-    
+    
+@router.delete("/users/{user_id}")
+def delete_user(req: Request, user_id: str, db: Session = Depends(get_db)):
+    admin = require_admin(req, db)
+
+    if admin.id == user_id:
+        raise HTTPException(400, "cannot delete yourself")
+
+    u = db.query(User).filter(User.id == user_id).first()
+    if not u:
+        raise HTTPException(404, "not found")
+
+    if u.role == Role.admin.value:
+        raise HTTPException(400, "cannot delete admin user")
+
+    # soft delete
+    u.disabled = True
+    db.add(u)
+    db.commit()
+    return {"ok": True}

backend/app/routes/auth.py

@@ -40,7 +40,8 @@ def me(req: Request, db: Session = Depends(get_db)):
     user = db.query(User).filter(User.id == uid).first()
     if not user:
         raise HTTPException(status_code=401, detail="not logged in")
-    return {"id": user.id, "email": user.email, "role": user.role, "theme_key": user.theme_key}
+    return {"id": user.id, "email": user.email, "role": user.role, "display_name": user.display_name}
+    
 
 
 @router.patch("/password")