Use canonical agent skills

[kpeez]

Use ~/.agents/skills as the canonical Agent Skills install location and remove the stale provider-specific orchestration skill copies.

Summary

• Installs shared skills once into ~/.agents/skills.
• Mirrors canonical skills only for providers that need provider-local skill directories.
• Removes Claude/Codex subagent-orchestrator skill trees for a later local-model rewrite.

Why

• The setup should have one canonical skills source instead of duplicating provider-specific copies as the primary model.
• Copilot already supports personal skills in ~/.agents/skills.
• The provider-specific subagent-orchestrator skills are intentionally being retired for now.

Changes

• Update scripts/setup-agent.sh to refresh ~/.agents/skills, mirror Codex/Claude/Gemini, and skip Copilot's provider-local mirror.
• Update README and provider addenda to document canonical skills and mirror behavior.
• Remove the Claude and Codex subagent-orchestrator skill trees.
• Remove subagent-orchestrator from the README skill list.

Testing

• PYTHONDONTWRITEBYTECODE=1 python3 specs/canonical-agent-skills/examples/canonical_skill_install.py
• bash -n scripts/setup-agent.sh
• PYTHONDONTWRITEBYTECODE=1 python3 -c 'import ast, pathlib, sys; [ast.parse(pathlib.Path(p).read_text(), filename=p) for p in sys.argv[1:]]' scripts/apply-auto-approval-configs.py specs/canonical-agent-skills/examples/canonical_skill_install.py
• git diff --check