Keyboard Navigation: Disabled "Go Back" Button in Reference Side Docs Receives Keyboard Focus

Describe the bug
When navigating via keyboard in the Reference side docs, the disabled "Go Back" button is included in the keyboard tab order and can receive keyboard focus even though it is unavailable and cannot be activated.

Steps to reproduce the behavior:

1. Navigate to Microsoft MakeCode for micro:bit.
2. Open an existing project or create a new one.
3. Press Tab to focus the Help button and press Enter.
4. Use the Down Arrow key to select Reference, then press Enter to open the Reference side docs.
5. Press Tab until focus reaches the external link icon.
6. Press Tab again.
7. Observe that focus moves to the disabled "Go Back" button.

Actual behavior
The disabled "Go Back" button is included in the keyboard tab order and can receive focus even though it is unavailable and cannot be activated.

Expected behavior
Disabled controls should be removed from the keyboard tab order and should not receive keyboard focus unless there is a specific accessibility reason for them to remain focusable.

Screenshots

Additional context
1.OS: Windows 11 25H2 & Mac Mini M2 macOS Tahoe 26.5.2
2.Browser: Chrome, Edge, Firefox, and Safari
3.makecode.microbit.org version: 9.0.3
4.Microsoft MakeCode version: 13.0.3

Start by reproducing the issue in the Reference side docs using the keyboard sequence described, focusing on the external-link icon and disabled Go Back button. Trace the Reference side-docs navigation entry point to find where that button is rendered and how its disabled state affects focus. Done means the disabled Go Back button is skipped in the tab order while the reported navigation still works.