The prompt (prompt.md) should be editable. Once it's edited, it should be saved to chrome sync storage and applied for future use (the default one should be ignored). Add a button at top with the label "Edit prompt". When the user clicks it, it opens a modal that loads a Textarea so that user can update and save it. It should load the default prompt when it's empty. You can load the default prompt by using import { promptTemplate } from './lib'. The prompTemplate in app.tsx needs to be updated.