Document and package the agent harness

[aryamantodkar]

Summary

• add AGENT_HARNESS.md with coordinator and specialist roles, plan routing, CodeGraph, RTK output recovery, bootstrap, and validation profiles
• copy the codebase-design, domain-modeling, and tdd skills from the sibling Premove repository
• connect the remaining skills to AGENTS.md and the architect and implementer instructions
• keep independent review in the configured reviewer agent without a separate code-review skill
• track .agents/skills/ while keeping other .agents state ignored
• link the guide from CONTRIBUTING.md

Why

The harness needs a concise operator guide and reusable design, domain-modeling, and test-first guidance. The configured roles handle execution and independent review.

Invariants

• AGENTS.md remains the source for routing authority and repository policies.
• Skills follow the four configured roles and accepted-plan rules.
• Local CodeGraph and RTK state stays out of Git.

Validation

• uv run --locked python scripts/agent/check.py focused --pytest tests/test_docs_routes.py
• parsed .codex/config.toml and all .codex/agents/*.toml files with Python tomllib
• git diff --check