Summary

• Add crabcode upgrade to compare the running version with the latest GitHub release.
• Run the cargo-dist shell installer only when an update is available, surfacing network, version, and installer failures.
• Enable cargo-dist shell installer artifacts so released binaries can self-upgrade.

Testing

• cargo fmt
• cargo test upgrade::tests
• cargo test parses_upgrade_command
• cargo run -- upgrade --help
• git diff --check

Notes

• The command targets GitHub releases for Blankeos/crabcode.
• Windows reports that automatic upgrades are unavailable rather than attempting the POSIX shell installer.