refactor: improve EventModal UI labels and visibility controls

- Rename 'Alarm' to 'Notification' for better clarity
- Rename 'Attendees' to 'Participants' with updated placeholder text
- Replace 'Visibility' dropdown with 'Visible to' toggle buttons (All/Participants)
- Remove CONFIDENTIAL option, keep only PUBLIC and PRIVATE
- Add icons (PublicIcon/LockIcon) with fixed sizing for toggle buttons
- Rename 'Show as' to 'Show me as'
- Fix ResponsiveDialog scroll bar positioning in expanded mode
- Update PeopleSearch placeholder to 'Start typing a name or email'

src/components/Attendees/PeopleSearch.tsx

@@ -102,8 +102,8 @@ export function PeopleSearch({
           {...params}
           error={!!error}
           helperText={error}
-          placeholder="Search user"
-          label="Search user"
+          placeholder="Start typing a name or email"
+          label="Start typing a name or email"
           onKeyDown={(e) => {
             if (e.key === "Enter" && onToggleEventPreview) {
               e.preventDefault();