Fix cursor display on higher resolutions - #70

Summary

The in-game interface is laid out in fixed pixels, so at the higher render
resolutions OpenTS supports the sidebar, tab bar, dialogs, and readouts stay
the same on-screen size while only the tactical view grows. This adds a
configurable interface scale so the UI can be enlarged to match the resolution
without giving up the wider tactical view.

Add [Video] UIScale (an integer multiplier, default 1) and scale the sidebar,
tab bar, radar, dialogs, and their text by that factor. The tactical view keeps
the full render resolution and is shrunk only by the extra width the scaled
sidebar occupies.

Behavior and compatibility

Presentation-only. The UI layout is not part of the deterministic simulation,
the save format, or network packets. Confirm that the sidebar's serialized
state (SidebarClass::Serialize and StripClass::Serialize) persists only
slot indices and scroll positions in slot units, never scaled pixel values.

Validation

• Configured with CMake 4.4.3, generator Visual Studio 17 2022, -A Win32 (MSVC 19.44.35207).
• Win32 Debug build: succeeded (GameD.exe).
• Win32 Release build: succeeded (Game.exe).
• CTest, Debug: 1/1 passed (logstress).

Documentation

• manual/changes/cursor-size-cap.md
• manual/changes/cursor-dialog-visibility.md
• manual/content/keys/cursorscale.md — notes the system-cursor size cap.

Checklist

• The change is focused; unrelated mechanical cleanup is separate
• Compatibility effects and any migration are explicit
• A player- or modder-visible engine change carries its change record
• Validation distinguishes what passed, failed, and was not run
• No prohibited assets, binaries, SDKs, credentials, or generated output are included