Add seal

[stefan-mysten]

Summary

• add seal as a supported standalone binary, including registry coverage and README updates
• make standalone release installs tolerant of linux/ubuntu, arm64/aarch64, and -vX.Y.Z tag formats while keeping stored versions normalized to vX.Y.Z
• stabilize the doctor env-var tests and verify the standalone path with focused unit and integration coverage

Testing

cargo test --lib
cargo test --test commands_test
cargo test test_default_mvr_workflow --test integration_test
cargo test test_update_workflow --test integration_test