Add a shopping list feature for groceries

[Copilot]

Adds a full shopping list feature to the app so users can manage grocery and other shopping items.

Changes Made

• src/storage.ts: Added ShoppingItem interface (id, name, optional quantity, completed, createdDate), added shoppingList: ShoppingItem[] to AppData, updated createInitialData() and buildMigratedData() to include the new field, and added five CRUD methods: addShoppingItem, updateShoppingItem, deleteShoppingItem, getShoppingItems, and clearCompletedShoppingItems.
• index.html: Added a 🛒 Shopping navigation tab and a full tab section with a shopping list container, empty-state message, and an Add/Edit modal with an item name (required) and quantity (optional) field.
• src/app.ts: Imported ShoppingItem, added currentEditingShoppingItemId state, registered event listeners, wired up shopping in switchTab(), and implemented renderShoppingList, renderShoppingItem, openShoppingItemModal, closeShoppingItemModal, saveShoppingItem, deleteShoppingItem, and clearCompletedShoppingItems methods.
• css/styles.css: Added shopping list styles consistent with the existing design system, including a responsive mobile breakpoint.
• tests/storage.test.ts: Added 10 unit tests covering all CRUD operations for the shopping list.

Features

• Add items with a name and an optional quantity
• Check items off as collected (strikethrough + dimmed styling)
• Edit or delete existing items via a modal
• "Clear Checked" button removes all completed items at once
• Data persisted to localStorage with full migration support for existing data

Testing

• ✅ TypeScript compilation passes
• ✅ All 97 unit tests pass
• ✅ Manual UI verification confirmed

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add a shopping list feature</issue_title>
<issue_description>Users would like to add a simple shopping list features for things like groceries. This can be lists with simple items that are checked off.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add a shopping list feature #56

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[JoeProgrammer88]

@copilot try again

[Copilot]

@copilot try again

The shopping list feature is fully implemented. Here's what was added:

• 🛒 Shopping tab in the navigation
• Add items with an optional quantity field
• Check off items as collected (strikethrough + dimmed styling)
• Edit & delete existing items via a modal
• Clear Checked button to remove all completed items at once
• Data is persisted to localStorage via the existing StorageManager pattern, with full migration support for existing data
• 10 new unit tests covering all CRUD operations