Feature request: align user skills discovery with OpenAI Codex "USER" scope ($HOME/.agents/skills)

[Fullstop000]

OpenAI Codex defines $HOME/.agents/skills as the standard USER scope for personal skills (docs).

Kimi-cli currently lists ~/.agents/skills in get_user_skills_dir_candidates(), but resolve_skills_roots() stops at the first existing candidate. This means if a user has both ~/.config/agents/skills and ~/.agents/skills, only the former is loaded.

Requested changes:

1. Load all existing user-scope skill directories instead of just the first one.
2. Walk up the directory tree for project-level discovery (from work_dir to the Git repo root), matching Codex REPO scope behavior.
3. (Optional) Add an admin/system scope such as /etc/kimi/skills.

This would improve interoperability for users coming from Codex and make $HOME/.agents/skills work reliably as a personal skills folder.