Add run alias for open command

[Abhinav-0311]

Fixes #38.

Summary

• Registers
  un as an alias for the existing open command so headless/batchmode scripts can use clearer wording.
• Adds the alias to zsh completion output with the same options as open.
• Documents ucll run ... -- -batchmode -quit in the README.
• Adds command-app tests covering the alias in help and the shared open-command options.

Testing

• git diff --check
• Not run: dotnet test src/ucll.tests -v minimal because dotnet is not installed on PATH in this environment.