Defer edit-mode font switch to next frame via RequestLoadFont() to
avoid modifying the locked ImFontAtlas between NewFrame() and Render().
Rework Nix packaging: split nativeBuildInputs/buildInputs correctly,
add devShells for nix develop, desktop file for kge, per-variant pname
and meta.mainProgram, and an overlay for NixOS configs.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
- Added `QtFrontend`, `QtRenderer`, and `QtInputHandler` for Qt-based UI rendering and input handling.
- Implemented support for theming, font customization, and palette overrides in GUITheme.
- Renamed and refactored ImGui-specific components (e.g., `GUIRenderer` -> `ImGuiRenderer`).
- Added cross-frontend integration for commands and visual font picker.
