fix: harden admin access, repair ORM joins, and add migration/tests

app/services/ctt_scoring.py

@@ -14,7 +14,7 @@ import math
 from datetime import datetime, timezone
 from typing import Optional
 
-from sqlalchemy import func, select
+from sqlalchemy import Integer, cast, func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.models.item import Item
@@ -190,7 +190,7 @@ async def calculate_ctt_p_for_item(
     result = await db.execute(
         select(
             func.count().label("total"),
-            func.sum(func.cast(UserAnswer.is_correct, type_=func.INTEGER)).label("correct"),
+            func.sum(cast(UserAnswer.is_correct, Integer)).label("correct"),
         ).where(UserAnswer.item_id == item_id)
     )
     row = result.first()