Enhance Cospend with debt breakdown and predefined users

- Add EnhancedBalance component with integrated single-user debt display
- Create DebtBreakdown component for multi-user debt overview
- Add predefined users configuration (alexander, anna)
- Implement personal + equal split payment method
- Add profile pictures throughout payment interfaces
- Integrate debt information with profile pictures in balance view
- Auto-hide debt breakdown when single user (shows in balance instead)
- Support both manual and predefined user management modes

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

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

src/lib/components/PaymentModal.svelte

@@ -79,6 +79,8 @@
       return `Split equally among ${payment.splits.length} people`;
     } else if (payment.splitMethod === 'full') {
       return `Paid in full by ${payment.paidBy}`;
+    } else if (payment.splitMethod === 'personal_equal') {
+      return `Personal amounts + equal split among ${payment.splits.length} people`;
     } else {
       return `Custom split among ${payment.splits.length} people`;
     }