This PR adds a button to close the panel when it is docked to the
bottom. Effectively, the button triggers the same `ToggleBottomDock`
action that clicking on the button that opened the panel triggers, but I
think having it there just makes it extra obvious how to close it, which
is beneficial.

As a bonus, also fixed the panel controls container height when it is
docked to the sides, so it perfectly aligns with the panel tabbar
height.

| Perfectly Aligned Header | Close Button |
|--------|--------|
| <img width="2620" height="2010" alt="Screenshot 2025-11-24 at 12  01
2@2x"
src="https://github.com/user-attachments/assets/08a50858-1b50-4ebd-af7a-c5dae32cf4f6"
/> | <img width="2620" height="2010" alt="Screenshot 2025-11-24 at 12 
01@2x"
src="https://github.com/user-attachments/assets/17a6eee0-9934-4949-8741-fffd5b106e95"
/> |

Release Notes:

- N/A