feat: drag-and-drop meal scheduling + 7-day grid

backend/app/api/meals.py

@@ -319,4 +319,45 @@ def swap_meal_item(item_id: UUID, new_recipe_id: UUID, db: Session = Depends(get
     item.denial_details = None
 
     db.commit()
-    return {"message": "Meal swapped", "item": item}
+    return {"message": "Meal swapped", "item": item}
+
+
+@router.put("/items/{item_id}/move")
+def move_meal_item(
+    item_id: UUID,
+    new_day_of_week: int,
+    new_meal_type: str,
+    db: Session = Depends(get_db),
+):
+    """Move a meal to a new day/type slot.
+
+    If the target slot is occupied by another item in the same meal plan,
+    swap the two items.
+    """
+    item = db.query(MealPlanItem).filter(MealPlanItem.id == item_id).first()
+    if not item:
+        raise HTTPException(status_code=404, detail="Meal plan item not found")
+
+    plan_id = item.meal_plan_id
+    conflict = (
+        db.query(MealPlanItem)
+        .filter(
+            MealPlanItem.meal_plan_id == plan_id,
+            MealPlanItem.day_of_week == new_day_of_week,
+            MealPlanItem.meal_type == new_meal_type,
+            MealPlanItem.id != item_id,
+        )
+        .first()
+    )
+
+    if conflict:
+        # swap day/type
+        conflict.day_of_week = item.day_of_week
+        conflict.meal_type = item.meal_type
+
+    item.day_of_week = new_day_of_week
+    item.meal_type = new_meal_type
+
+    db.commit()
+    db.refresh(item)
+    return {"message": "Meal moved", "item": item}