Add sop-onboard skill and agent for project onboarding

[ldraney]

Summary

Add a new skill (/sop-onboard) and agent (sop-onboard) to dev-sop-engine that enables autonomous onboarding of any project into the dev-sop-engine system.

Details

Skill: /sop-onboard

Step-by-step playbook covering:

• Prerequisites (git repo, sop_generate MCP tool or npx)
• Full workflow: analyze project → create issue → branch → scaffold sop/ → author sop.json → run generator → verify → commit → PR
• Minimal sop.json starter template with tailoring guidelines
• Troubleshooting section

Agent: sop-onboard

Autonomous onboarding agent that:

• Uses /sop-onboard skill as its playbook
• Decides when to add rules, MCP servers, skills, agents
• Has tools: Read, Glob, Grep, Edit, Write, Bash

Test Plan

• .claude/skills/sop-onboard/SKILL.md exists with correct content
• .claude/agents/sop-onboard.md has YAML frontmatter
• Test on ~/ebay-sdk as real-world validation