[Feature]: Toggle Splitscreen Hotkey. Track a Unit in split screen view

### Describe the Feature

By default, there is a key for full screen and a key for split screen. Having to use two binds is absurd. Additionally there is track a unit in primary view and track a unit on second monitor. But no track unit in splitscreen iew
This feature would just add a key that toggles between screen settings and another hotkey to track a unit in splitscreen view.

### Expected Behavior

Hotkey under UI category, that toggles split screen.
Hotkey under Camera catergory, that Tracks a unit in splitscreen view

### Screenshots

### Additional context

I made a personal UI mod for this, and it seems like a simple thing to be integrated. I can do the PR this week.

Start by locating the existing full-screen and split-screen hotkey handlers, then inspect the primary-view and second-monitor unit-tracking behavior. Add the requested UI toggle and Camera-category split-screen tracking hotkeys. Done means each action works from its assigned binding and the existing screen and tracking behavior remains unchanged.

Written by the indexing model from the issue text.