Add payment categories with emoji icons and image upload support

- Add comprehensive category system: Groceries 🛒, Shopping 🛍️, Travel 🚆, Restaurant 🍽️, Utilities ⚡, Fun 🎉
- Create category utility functions with emoji and display name helpers
- Update Payment model and API validation to support categories
- Add category selectors to payment creation and edit forms
- Display category emojis prominently across all UI components:
  - Dashboard recent activities with category icons and names
  - Payment cards showing category in metadata
  - Payment modals and view pages with category information
- Add image upload/removal functionality to payment edit form
- Maintain responsive design and consistent styling across all components

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/routes/api/cospend/payments/[id]/+server.ts

@@ -61,6 +61,7 @@ export const PUT: RequestHandler = async ({ params, request, locals }) => {
         paidBy: data.paidBy,
         date: data.date ? new Date(data.date) : payment.date,
         image: data.image,
+        category: data.category || payment.category,
         splitMethod: data.splitMethod
       },
       { new: true }