v2.10.1 — First-class Codex discovery

Codex compatibility\n\n- Adds a root AGENTS.md for repository-wide Codex guidance.\n- Exposes all 19 canonical StyleSeed skills through repo-scoped .agents/skills without duplicating their source.\n- Documents Codex invocation as $ss-* or the Skills picker, while Claude Code continues to use /ss-*.\n- Adds Codex-specific manual install and update paths in the English and Korean docs.\n- Corrects stale skill counts across engine and contributor documentation.\n\n## Verified\n\n- A fresh Codex session discovered all 19 repo skills.\n- $ss-score loaded the canonical engine/.claude/skills/ss-score/SKILL.md.\n- The Next.js production build passed for all 113 generated routes.\n\nPR #4 is not included in this release.