Adds Hugging Face's official skill catalog to the default GitHub taps and
classifies it as a trusted source alongside openai/skills and anthropics/skills.
- tools/skills_guard.py: huggingface/skills -> TRUSTED_REPOS
- tools/skills_hub.py: GitHubSource.DEFAULT_TAPS += huggingface/skills (skills/)
- website/docs: list it under default taps + trusted-source examples
Closes#2549.
Co-authored-by: teknium1 <127238744+teknium1@users.noreply.github.com>