feat(shopping): toggleCheck (idempotent)

Idempotentes Setzen/Loeschen von shopping_cart_check-Eintraegen
ueber (name_key, unit_key). Check ueberlebt Recipe-Removals,
solange ein anderes Rezept weiterhin zur Zeile beitraegt —
verifiziert durch 3 neue Integrationstests (17 total).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/integration/shopping-repository.test.ts

@@ -5,7 +5,8 @@ import {
   addRecipeToCart,
   removeRecipeFromCart,
   listShoppingList,
-  setCartServings
+  setCartServings,
+  toggleCheck
 } from '../../src/lib/server/shopping/repository';
 import type { Recipe } from '../../src/lib/types';
 
@@ -185,3 +186,48 @@ describe('listShoppingList aggregation', () => {
     expect(rows[0].total_quantity).toBeNull();
   });
 });
+
+describe('toggleCheck', () => {
+  function setupOneRowCart() {
+    const db = openInMemoryForTest();
+    const id = insertRecipe(db, recipe({
+      ingredients: [{ position: 1, quantity: 200, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    addRecipeToCart(db, id, null);
+    return { db, id };
+  }
+
+  it('marks a row as checked', () => {
+    const { db } = setupOneRowCart();
+    toggleCheck(db, 'mehl', 'g', true);
+    const rows = listShoppingList(db).rows;
+    expect(rows[0].checked).toBe(1);
+  });
+
+  it('unchecks a row when passed false', () => {
+    const { db } = setupOneRowCart();
+    toggleCheck(db, 'mehl', 'g', true);
+    toggleCheck(db, 'mehl', 'g', false);
+    expect(listShoppingList(db).rows[0].checked).toBe(0);
+  });
+
+  it('check survives removal of one recipe when another still contributes', () => {
+    const db = openInMemoryForTest();
+    const a = insertRecipe(db, recipe({
+      title: 'A',
+      ingredients: [{ position: 1, quantity: 100, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    const b = insertRecipe(db, recipe({
+      title: 'B',
+      ingredients: [{ position: 1, quantity: 200, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    addRecipeToCart(db, a, null);
+    addRecipeToCart(db, b, null);
+    toggleCheck(db, 'mehl', 'g', true);
+    // Rezept A weg, Mehl kommt noch aus B — check bleibt, mit neuer Menge
+    removeRecipeFromCart(db, a);
+    const rows = listShoppingList(db).rows;
+    expect(rows[0].checked).toBe(1);
+    expect(rows[0].total_quantity).toBe(200);
+  });
+});