agents-cli: reflect the hf-cli skill auto-install

[davanstrien]

huggingface_hub v1.27.0 changed how the hf-cli skill gets installed, and agents-cli.md still describes the old flow. The release notes link to this page, so it's the first thing a reader lands on.

huggingface/huggingface_hub#4608
https://github.com/huggingface/huggingface_hub/releases/tag/v1.27.0

What changed here:

• The standalone installer now installs the Skill globally (including the Claude Code location), so that's stated up front, with --exclude-skill / -ExcludeSkill to opt out.
• "Add the CLI Skill" is reframed as the path for people the installer doesn't cover — pip, Homebrew, opting out, or wanting it in one project.
• The tip said the Skill is "always up to date". That is now the opposite of true: it's generated at install time, and v1.27.0 ships a once-a-day reminder precisely because it drifts. Replaced with how to refresh it (hf update, hf skills update -g) and how to silence the reminder.
• agent-traces.md told readers to run hf skills add right after the installer. That step is now redundant, so it links here instead.

The equivalent guidance landed in the huggingface_hub guides with #4608; this mirrors it in hub-docs.

Commands verified against v1.27.0, and the --exclude-skill / -ExcludeSkill flags against the deployed scripts at hf.co/cli/.

Unrelated but adjacent: #2539 is a one-line fix to this same file, approved since June 8 and still unmerged. Different line, no conflict.

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

[Pierrci]

thanks, lgtm!