feat: add team-harness Agent Skill

[fazpu]

Summary

• Adds .claude/skills/team-harness/SKILL.md — an Agent Skill that walks Claude through installing, configuring, and running team-harness with the right commands, env vars, and config recipes.
• Description is tuned to trigger on direct mentions (th, th init/run/repl/logs) and on intent (orchestrating multiple AI coding CLIs together).
• Covers: quickstart, worker CLI prerequisites table, th init sidecars, auth (OpenRouter / OpenAI-compatible / Codex subscription), REPL + headless + Python SDK usage, recipes for pinning models / reasoning effort / OpenRouter routing for codex + claude (with the gemini caveat), custom agent templates, common gotchas (OpenHands LLM_* leakage, Claude ANTHROPIC_DEFAULT_*_MODEL triple, removed template = "..." form). Defers the long tail to README.md.

Test plan

• Open a fresh Claude Code session in another repo (or this one) and ask "how do I install team-harness and run it against codex+claude only?" — confirm the skill triggers and the answer follows the install→th init→OPENROUTER_API_KEY th run path.
• Ask "how do I route claude through openrouter inside team-harness?" — confirm it returns the [agents.claude.provider_env] recipe with ANTHROPIC_API_KEY = "" and {env:OPENROUTER_API_KEY}.
• Ask something adjacent but unrelated (e.g. "set up a python project") — confirm the skill does not trigger.

🤖 Generated with Claude Code