install-tend

Run `npx skills use "https://github.com/max-sixty/tend" --skill "max-sixty/tend/install-tend"` and follow the generated skill instructions now. Read its complete output, redirecting it to a temporary file first if necessary. Resolve relative paths from the supporting-files directory it provides.

Use the skills in "https://github.com/max-sixty/tend" that are relevant to the current task. Run `npx skills add "https://github.com/max-sixty/tend"` and select the relevant skills, then follow their instructions.