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/RepeatEvent.test.tsx

@@ -102,8 +102,8 @@ async function setupEventPopover(
   const titleInput = screen.getByLabelText("Title");
   fireEvent.change(titleInput, { target: { value: "Meeting" } });
 
-  // Click Show More to expand the dialog
-  const showMoreButton = screen.getByText("Show More");
+  // Click More options to expand the dialog
+  const showMoreButton = screen.getByText("More options");
   fireEvent.click(showMoreButton);
 
   // Check Repeat checkbox to show repeat options