Add Thunderbird for Android to the main nav menu

Thunderbird for Android is not in the main "Ask a Question" nav menu, while we have an empty spot there. We should add TB for Android to that menu.

<img width="2524" height="836" alt="Image" src="https://github.com/user-attachments/assets/f4bd9fd1-97b1-44e7-9f7e-d888990b284c" />