Add CI/CD workflow for automated pipeline validation

[PAMulligan]

Summary

There are no GitHub Actions workflows for CI/CD. Scripts, templates, and configuration changes are merged without automated validation.

What Should Be Validated on PR

1. Script tests — run scripts/__tests__/ test suite
2. Agent YAML validation — verify all agents have valid frontmatter
3. Skill structure validation — verify skills follow expected format
4. Template validation — verify templates produce installable projects
5. Config validation — verify pipeline.config.json against schema (depends on Add JSON schema validation for pipeline.config.json #45)
6. Token verification — run verify-tokens.sh on any component changes
7. Lint & format — run lint-and-format.sh

Acceptance Criteria

• .github/workflows/ci.yml with PR trigger
• At minimum: lint, script tests, agent/skill validation
• Status checks required for merge on main branch
• Workflow runs in under 5 minutes