Cataclysm v0.8.0

Living-Earth simulator visual-system release: source-first desktop workflow, grouped reference events, instrumented Earth viewport, solver-aware transport, refined Settings/onboarding, and deterministic dark/light visual verification. All 153 unit tests, 23 browser checks, and 91 Rust release tests pass locally. Windows installers are currently unsigned because code-signing credentials are not configured; verify downloads with the attached SHA-256 checksums.