Add macOS support to install.sh

[Aaronontheweb]

Summary

The install script (scripts/install.sh) currently only supports Linux. macOS is rejected at the platform detection step:

case "$os" in
    linux) ;;
    *) echo "Error: Unsupported OS: $os. This script supports Linux only." >&2; exit 1 ;;
esac

Since macOS supports the same curl -sSL ... | bash install pattern, we should add darwin support with the appropriate .NET RIDs.

Proposed Change

Add a darwin case to detect_platform() in scripts/install.sh:

case "$os" in
    linux) ;;
    darwin) ;;
    *) echo "Error: Unsupported OS: $os." >&2; exit 1 ;;
esac

And add architecture mappings:

# For darwin:
case "$arch" in
    x86_64|amd64) rid="osx-x64" ;;
    aarch64|arm64) rid="osx-arm64" ;;
esac

Motivation

The netclaw.dev landing page install section should show macOS as a supported platform alongside Linux, Windows, and Docker. This is a prerequisite for that.