chore: add contributing guide and issue templates

[brainsparker]

Why

you.md has CI but no contributor documentation and no issue templates. A contributing guide lowers the bar for tool-integration PRs (the most likely community contribution), and structured issue forms capture version, environment, and a minimal profile up front instead of over several comment round trips.

What changed

• CONTRIBUTING.md: dev setup, offline test policy, project layout, a checklist for adding new AI tool integrations to the skill installer, PR expectations, and a note that protocol changes should start as issues
• .github/ISSUE_TEMPLATE/bug_report.yml: version, environment, affected area, repro, and minimal profile fields
• .github/ISSUE_TEMPLATE/feature_request.yml: request kind, problem, proposal, alternatives

Validation

• Both issue forms are yaml syntax-validated
• CONTRIBUTING instructions verified in a clean environment: npm install, build, npm test (145/145), and npm run lint all work as documented