feat: ship /wt as an agent skill installable via npx skills

[johnpangalos]

What

Converts the claude/commands/wt.md slash-command file into a proper agent skill at skills/wt/SKILL.md, and documents installation via Vercel's skills CLI:

npx skills add johnpangalos/wt

Why

• The skills/<name>/SKILL.md layout is what npx skills add auto-discovers, so anyone can install the skill into Claude Code, Cursor, Codex, OpenCode, etc. — no more hand-copying a command file.
• Unlike a slash command (fires only when the user types /wt), a skill's frontmatter description lets agents invoke it on their own — e.g. after git worktree add, the agent knows to run wt switch <branch> to pop a Ghostty tab. In Claude Code it stays user-invocable as /wt too.

Changes

• Add skills/wt/SKILL.md (content carried over from the command file, plus trigger-oriented frontmatter, agent-aware wt list note, and an install hint for missing wt)
• Remove claude/commands/wt.md
• Rewrite the README's "From Claude Code" section as "Agent skill (Claude Code & friends)" with npx skills add instructions and a manual-copy fallback

Verified

pnpm dlx skills add . --list discovers exactly one skill (wt) with the intended description.

🤖 Generated with Claude Code