Validate a Signup Form

Elements are provided: form, usernameInput (a text field), emailInput, and errorBox. Build the submit flow: 1. Add a submit listener to form that calls event.preventDefault() first. 2. Read the username; if its trimmed length is under 3, set errorBox.textContent to a helpful message and stop. 3. Read the email; if it does not include "@", show an error the same way. 4. Otherwise clear errorBox.textContent and log Welcome, <username>. Then simulate: submit with username "ab" (too short), then submit with a valid username and email — and log after each.

Difficulty: intermediate