Previously the Install step hard-coded 'review-bot-linux-amd64'. This fails on arm64 runners (Graviton, Apple Silicon) where uname -m returns 'aarch64' or 'arm64'. Changes: - Add OS/arch detection in 'Determine version' step using uname -s/-m - Map uname output to asset name format: x86_64→amd64, aarch64/arm64→arm64, linux→linux, darwin→darwin - Emit 'os' and 'arch' as step outputs alongside 'version' - Update cache key: review-bot-{os}-{arch}-{version} - Update Install step: BINARY derived from step outputs - Anchor checksum grep to exact filename (not substring match) - Unsupported OS or arch exits with a clear error message Supported platforms: linux-amd64, linux-arm64, darwin-amd64, darwin-arm64 (matches what the release workflow builds)
