fix(gui): use Fyne black screen for controller flow

[ioerrors]

This PR keeps black-screen behavior in the main Fyne window when entered from the main menu, instead of routing that path through the SDL input window.

Why:

• In gaming-mode controller-first use, opening the SDL input window for black screen can be counterproductive.
• It can change touch behavior and interfere with controller passthrough expectations.
• Controller-first black screen is conceptually a simple UI state change, so Fyne is a better fit for that entry path.

What changed:

• Main-menu Black Screen now swaps to a Fyne full-screen black view.
• Tap restores the previous main content.
• Cursor hiding/transition behavior is handled in the Fyne path for cleaner UX. (I use cursor hiding on button hover so no cursor lingers)

What did not change:

• SDL keyboard/mouse workflow remains intact.
• No protocol/daemon/auth changes in this PR.

Testing:

• Built and tested on Steam Deck in gaming mode (non-Steam app launch).
• Verified controller-first black screen entry/exit behavior is stable.

Notes:

• This is intended as one half of a split approach:
• SDL black screen for keyboard path
• Fyne black screen for controller-first path

[Lucaber]

Did you enable touch support in SteamInput: https://github.com/Lucaber/deckjoy#steam-input

[ioerrors]

I did not mess with any SteamInput settings; my goal with my PRs on this project was to reduce friction as much as possible, but perhaps a bit tunnel visioned on my use case (controller mode no keyboard, non-steam app launch from gaming mode, for use with games like cyberpunk2077).

It's possible the issue I saw with SDL based path entering black screen from main UI black screen option came from not changing any SteamInput settings. This fyne implementation works for my workflow b/c it requires no steps to setup, but maybe for games that require the touchscreen or if you're using the keyboard in the touchscreen SDL is the right path?