Turns demo targets into Playwright selectors.

• "#post_title": any CSS or Playwright selector string, used as-is
• {:link, "New Post"}: a link with that accessible name
• {:button, "Save"}: a button with that accessible name
• {:label, "Title"}: the form control for that label
• {:text, "Hello"}: an element containing that text
• {:role, "heading", "Posts"}: any ARIA role and name

Name matching is case-insensitive and substring-based (Playwright's default) unless you pass exact: true as a third element, e.g. {:link, "Post", exact: true}.