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/config/users.ts

@@ -0,0 +1,16 @@
+// Predefined users configuration for Cospend
+// When this array has exactly 2 users, the system will always split between them
+// For more users, manual selection is allowed
+
+export const PREDEFINED_USERS = [
+  'alexander',
+  'anna'
+];
+
+export function isPredefinedUsersMode(): boolean {
+  return PREDEFINED_USERS.length === 2;
+}
+
+export function getAvailableUsers(): string[] {
+  return [...PREDEFINED_USERS];
+}