refactor(apps): simplify API layer by removing redundant wrapper classes

- Remove ApiClientWrapper and MockApiClientWrapper
- Simplify IApiClient interface
- Update dependency injection configuration
- Optimize calendar service and AG-UI chat models

apps/lib/features/calendar/ui/screens/calendar_month_screen.dart

@@ -304,7 +304,7 @@ class _CalendarMonthScreenState extends State<CalendarMonthScreen> {
                         vertical: 2,
                       ),
                       decoration: BoxDecoration(
-                        color: color.withOpacity(0.2),
+                        color: color.withValues(alpha: 0.2),
                         borderRadius: BorderRadius.circular(4),
                       ),
                       child: Text(

apps/lib/features/calendar/ui/widgets/create_event_sheet.dart

@@ -368,7 +368,7 @@ class _CreateEventSheetState extends State<CreateEventSheet>
         Row(
           children: defaultColors.map((color) {
             final colorHex =
-                '#${color.value.toRadixString(16).substring(2).toUpperCase()}';
+                '#${color.toARGB32().toRadixString(16).substring(2).toUpperCase()}';
             final isSelected = _selectedColor == colorHex;
             return GestureDetector(
               onTap: () => setState(() => _selectedColor = colorHex),