Bootstrap agent skills from dotfiles

[dgalarza]

Summary

• Move public skills from .claude/skills to .agents/skills for agent-shared loading
• Update setup-claude.sh to link public and vault skills into ~/.agents/skills while keeping CLAUDE.md in ~/.claude
• Mirror installed ~/.agents/skills entries into ~/.claude/skills for Claude Code compatibility
• Migrate the old create-command slash command into a create-skill agent skill
• Update docs and a few legacy skill paths to reference ~/.agents/skills
• Keep first-machine bootstrap fixes for Atuin and the tmux Catppuccin plugin path

Verification

• bash -n setup-claude.sh
• ./setup-claude.sh linked 42 public skills and 10 private vault skills
• ./setup-claude.sh mirrored 52 skills into ~/.claude/skills
• Checked ~/.agents/skills and ~/.claude/skills for broken symlinks