Fix: preserve half screen mode when exiting commit filtering

[Xavrir]

Fixes #5179

When filtering commits, lazygit automatically switches to half-screen mode if the user is in normal mode. However, when exiting the filter, it was unconditionally resetting to normal mode, even if the user had configured half-screen mode as their default.

This fix tracks whether filtering forced the screen mode change. On exit, it only restores normal mode if the half-screen mode was forced by filtering, preserving any user-configured half-screen preference.

Changes:

• Track forced half-screen mode in the filtering state
• Only restore normal mode on filter exit if half-screen was forced
• Add unit test covering the screen mode restoration logic
• Add integration test verifying the behavior with configured half-screen mode