Install Plannotator command skills under Codex home

[backnotprop]

Summary

• install only the command-overlap Plannotator skills into ~/.codex/skills: plannotator-review, plannotator-annotate, and plannotator-last
• remove those command-overlap skills from the legacy shared ~/.agents/skills scope so they no longer collide with slash commands
• keep shared-agent Plannotator skills, including plannotator-setup-goal, in ~/.agents/skills and remove stale Codex copies of those shared-agent skills
• avoid treating an installer-created ~/.codex/skills directory as proof that Codex hooks should be configured
• copy skill directories only when present so version-pinned installs against older tags do not fail on missing newer skills
• keep Claude skill install behavior unchanged and assert command-overlap skills include OpenAI config

Tests

• bash -n scripts/install.sh
• git diff --check
• bun test scripts/install.test.ts
• temp-dir copy simulation against v0.17.10, v0.19.7, and HEAD