Task partially completed:

✅ Successfully navigated to IMDb Top 250 movies list
✅ Identified #1 movie: 'The Shawshank Redemption' (1994) - Rating: 9.3/10
❌ Could NOT add movie to watchlist

Reason for failure: Adding movies to watchlist requires user authentication (sign-in). The Watchlist button redirected me to a sign-in page with options for IMDb/Amazon/Google/Apple login, but no credentials were provided.

To complete this task, you would need to either:
1. Provide IMDb login credentials
2. Manually sign in at imdb.com and then add movies from your watchlist