Build a like button with optimistic update

• Shows the like state (liked or not) and the count; clicking toggles both immediately, before the request finishes
• A mock likePost(id, liked) call returns after a delay and sometimes fails (make the failure rate configurable)
• On failure the UI rolls back to the previous state and shows an error message that can be dismissed or retried
• While a request is in flight, further clicks are ignored or coalesced so a double click cannot send duplicate requests
• Loading and error states are visible (for example a subtle pending style and an aria-live message)
• The button is a real button with aria-pressed and an accessible label that includes the count

Only after every requirement works.

• Coalesce rapid toggles so that only the final intended state is sent
• Handle an out-of-order response by ignoring responses from stale requests
• Reconcile the count with the server value returned in the response