feat: integrate main's EventDisplayPreview UI with EventUpdateModal

1. Replace old EventDisplayPreview with main's new Figma UI
   - Use ResponsiveDialog instead of Popover
   - Keep file at features/Events/ location (not components/Event/)
   - Integrate InfoRow, EditModeDialog components from main
   - Fix all imports to work with new location

2. Add EventUpdateModal integration
   - Edit icon now opens EventUpdateModal instead of EventDisplayModal
   - EventUpdateModal uses shared EventFormFields component

3. Fix imports and exports
   - Use default import for ResponsiveDialog
   - Use named import for EditModeDialog
   - Fix anchorPosition to be optional with default value

4. Performance improvement
   - Open EventUpdateModal immediately without waiting for API
   - Let modal fetch fresh data in background via useEffect

5. Fix Checkbox styling warning
   - Use sx prop instead of style for nested MUI selectors
   - Fix 'Unsupported style property &.Mui-checked' console warning

src/components/Calendar/CalendarSelection.tsx

@@ -217,7 +217,7 @@ function CalendarSelector({
       <div>
         <label>
           <Checkbox
-            style={{
+            sx={{
               color: calendars[id].color,
               "&.Mui-checked": { color: calendars[id].color },
             }}