Click to edit UI (#385)

- [x] add e2e test - happy case (make sure it clears selection and next
prompt is empty, and preview is cleared); de-selection case
- [x] shim - old & new file
- [x] upgrade path
- [x] add docs
- [x] add try-catch to parser script
- [x] make it work for next.js
- [x] extract npm package
- [x] make sure plugin doesn't apply in prod

src/components/chat/ChatHeader.tsx

@@ -191,6 +191,7 @@ export function ChatHeader({
         </div>
 
         <button
+          data-testid="toggle-preview-panel-button"
           onClick={onTogglePreview}
           className="cursor-pointer p-2 hover:bg-(--background-lightest) rounded-md"
         >