Keep Open Wiki button visible while scrolling

Problem

The "Open Wiki" button appears near the top of the page. During wiki creation, users often scroll through the installation logs and need to scroll back to the top once the wiki is ready.

Approach

This patch keeps the "Open Wiki" action accessible by displaying the button as a fixed button at the bottom center of the viewport, ensuring it remains visible regardless of the scroll position.

The helper text was also updated to indicate that the button appears below.

Testing

• Created a wiki locally.
• Scrolled through the installation logs during wiki creation.
• Verified that the "Open Wiki" button remains visible while scrolling.
• Verified that the button remains clickable and centered.
• Verified the updated helper text.

Bug: T410442