Adds tooling/install-godot script that downloads the Godot binary
from GitHub releases to ~/bin/godot4. Skips download when the
correct version is already installed. Supports Linux x86_64/arm64
and macOS. GODOT_VERSION defaults to 4.6 and is overridable.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
