build(debug): add CMake option for debug cheats in release builds

[bobtista]

• closes Implement CMake option for _ALLOW_DEBUG_CHEATS_IN_RELEASE #1335

Summary

Implements a CMake option RTS_DEBUG_CHEATS to control debug cheat availability in release builds, replacing the manual DONT_ALLOW_DEBUG_CHEATS_IN_RELEASE define in GameCommon.h.

Usage

# Enable debug cheats in release builds
cmake -DRTS_DEBUG_CHEATS=ON ..

# Explicitly disable in all builds
cmake -DRTS_DEBUG_CHEATS=OFF ..

# Use default behavior (auto-enable in DEBUG builds only)
cmake -DRTS_DEBUG_CHEATS=DEFAULT ..