Navigation Bar

User story

As a user, I want to see a navigation bar with tabs for HTML, CSS, and JS, as well as a "Change View" button to switch between code and preview.

Acceptance criteria

• The navigation bar is displayed at the top of the screen with a purple background color.
• The HTML, CSS, and JS tabs are visible in the navigation bar.
• The "Change View" button is displayed on the right side of the navigation bar.
• The navigation bar and button are non-functional for now (no logic implemented).