Return helpdoc for single -h

[rolandwalker]

Description

-h alone cannot be a hostname specification, so when it is the only item in the list of arguments, respond with the helpdoc, matching the behavior of --help.

Previously, if the user ran

mycli -h

the response was only the cryptic

Error: Option '-h' requires an argument.

Checklist

• I added this contribution to the changelog.md file.
• I added my name to the AUTHORS file (or it's already there).
• To lint and format the code, I ran

  uv run ruff check && uv run ruff format && uv run mypy --install-types .

[github-actions]

1. Low: Missing end-to-end test for actual CLI behavior of mycli -h
   • Current tests only validate the helper function output (filtered_sys_argv) in test/test_main.py:156 and test/test_main.py:164.
   • They do not verify that invoking main() with sys.argv=['mycli','-h'] actually returns help text and exits successfully (the user-visible behavior this PR changes at mycli/main.py:2716).
   • Action: add an integration-style test that asserts -h and --help have equivalent outcome (exit code and help output), and that -h example.com still maps to host.

No correctness or security issues stood out in the code change itself.

Could not run tests in this environment because pytest is not installed (pytest: command not found).