Updated bundled runtime config payload from GTK2-style gtkrc to GTK3 settings.ini in the bundle manifest, and added a new osx/settings.ini with Mac theme/key-theme defaults and image settings.
Updated osx/launcher.sh to remove the GTK2-specific GTK2_RC_FILES usage, switch module file paths from gtk-2.0 to gtk-3.0, and add GTK3-appropriate GTK_THEME / GTK_KEY_THEME environment variables for macOS runtime behavior.
Checked the osx/ packaging scripts/manifests for other hardcoded GTK2 identifiers and confirmed none remain in that packaging scope after the migration.