feat(shopping): setCartServings mit Positiv-Validation

src/lib/server/shopping/repository.ts

@@ -55,11 +55,16 @@ export function removeRecipeFromCart(
 }
 
 export function setCartServings(
-  _db: Database.Database,
-  _recipeId: number,
-  _servings: number
+  db: Database.Database,
+  recipeId: number,
+  servings: number
 ): void {
-  throw new Error('not implemented');
+  if (!Number.isInteger(servings) || servings <= 0) {
+    throw new Error(`Invalid servings: ${servings}`);
+  }
+  db.prepare(
+    'UPDATE shopping_cart_recipe SET servings = ? WHERE recipe_id = ?'
+  ).run(servings, recipeId);
 }
 
 export function listShoppingList(db: Database.Database): ShoppingListSnapshot {