Stop installing redundant external skills

[chubes4]

Summary

• Stop cloning WordPress agent skills and Data Machine skills during wp-coding-agents skill sync.
• Keep only the two wp-coding-agents-owned skills: setup and upgrade.
• Clean unmanaged skill directories from runtime and Kimaki persistent skill stores so stale external skills do not keep returning.

Why

The composed AGENTS.md already provides the site-specific WordPress, Data Machine, and Homeboy operating context. Keeping separate static skills for those areas duplicates that context and can drift out of date.

Testing

• bash tests/post-upgrade-restore.sh
• ./upgrade.sh --skills-only --dry-run --wp-path '/Users/chubes/Studio/intelligence-chubes4'
• bash -n lib/skills.sh bridges/kimaki/post-upgrade.sh upgrade.sh setup.sh
• git diff --check

AI assistance

• AI assistance: Yes
• Tool(s): OpenCode (GPT-5.5)
• Used for: Drafted the implementation, updated tests/docs, and ran local verification; Chris provided the rationale and direction.