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

__test__/components/DuplicateEvent.test.tsx

@@ -95,6 +95,9 @@ describe("EventDuplication", () => {
 
     fireEvent.click(screen.getByText("Duplicate event"));
 
+    // Cancel button only appears in expanded mode
+    fireEvent.click(screen.getByText("More options"));
+
     fireEvent.click(screen.getByRole("button", { name: /Cancel/i }));
 
     expect(handleClose).toHaveBeenCalled();