TitleBar without any interactive element is still tab-navigable

### Describe the bug

TitleBar without any interactive element is still tab-navigable. Focus can land on the TitleBar even though there is nothing to interact with.

Ref: https://github.com/microsoft/PowerToys/issues/41944

### Why is this important?

It’s unintuitive for users, since a TitleBar with no interactive controls should not receive focus. This disrupts tab navigation flow and creates unnecessary stops, especially confusing for keyboard-only and screen reader users.

### Steps to reproduce the bug

[FocusableTitleBar.zip](https://github.com/user-attachments/files/22478258/FocusableTitleBar.zip)

1. Build & run the attached app.
2. Focus on the button.
3. Press Ctrl+Tab to navigate backward.
4. Expect the text box to be focused.
5. Be disappointed.
6. Watch the focus vanish into a black hole (or white hole, depending on the theme).

### Actual behavior

_No response_

### Expected behavior

_No response_

### Screenshots

_No response_

### NuGet package version

None

### Windows version

_No response_

### Additional context

_No response_