feat: add cross-file reference validator for CI
Add tools/validate-file-refs.js that validates cross-file references
in BMAD source files (agents, workflows, tasks, steps). Catches broken
file paths, missing referenced files, wrong extensions, and absolute
path leaks before they reach users.
Addresses broken-file-ref and path-handling bug classes which account
for 25% of all historical bugs (59 closed issues, 129+ comments).
- Scans src/ for YAML, markdown, and XML files
- Validates {project-root}/_bmad/ references against source tree
- Checks relative path references, exec attributes, invoke-task tags
- Detects absolute path leaks (/Users/, /home/, C:\)
- Adds validate:refs npm script and CI step in quality.yaml
a50679c5c4