Add favicon

[braboj]

As a visitor, I want to see a branded favicon so that the tutorial tab is recognizable in the browser.

What

Add a favicon to the tutorial page.

Why

Currently the page shows the default browser icon — looks unfinished and hurts brand recognition for codewithbranko.com.

Acceptance criteria

• Favicon displays in browser tab
• Works across major browsers (Chrome, Firefox, Safari, Edge)