chore: migrate AI skills to .agents directory

[denolfe]

Moves repository AI skills to .agents/skills so Codex can discover them. Claude Code keeps access through .claude/skills, a symbolic link that points to the new directory.

Before: .claude/skills/<name>/SKILL.md
After:  .agents/skills/<name>/SKILL.md
        .claude/skills -> ../.agents/skills

Key Changes

• Moved shared skills

  • The repository's seven AI skills now live under .agents/skills.

• Preserved Claude Code support

  • The .claude/skills link keeps the existing Claude Code discovery path working.

• Normalized skill metadata

  • All migrated skills now pass Codex validation. Tool-specific settings preserve manual invocation for audit-dependencies.

• Updated repository guidance

  • Contributor documentation and ignore rules now use .agents/skills as the primary location.

References / Links

• OpenAI skill documentation: documents .agents/skills discovery and Codex invocation policy.
• Claude Code skill documentation: documents .claude/skills discovery and linked skill directories.