feat: Update event modal UI with header icons and improved actions layout

- Add expand and close icons to ResponsiveDialog header in normal mode
- Change 'Show More' button to 'More options' with Add icon
- Hide Cancel button in normal mode, show only in extended mode
- Add showHeaderActions prop to ResponsiveDialog for UI control
- Preserve EventDisplayPreview modal with old UI (no header icons)
- Update all affected test cases to match new UI behavior

src/features/Events/EventDisplayPreview.tsx

@@ -115,6 +115,7 @@ export default function EventPreviewModal({
       <ResponsiveDialog
         open={open && !hidePreview}
         onClose={() => onClose({}, "backdropClick")}
+        showHeaderActions={false}
         style={{ overflow: "auto" }}
         title={
           event.title && (