feat: add ruleset validation script and run it in CI

[mkistler]

Summary

Adds automated validation for Spectral ruleset files against the official Spotlight ruleset schema.

Changes

• Added scripts/validate-ruleset.js to validate spectral.yaml and all aep/*.yaml files.
• Added the npm run validate script.
• Added schema references to the ruleset YAML files.
• Integrated validation into the CI workflow.
• Updated lint configuration and dependencies for the new script.

[toumorokoshi]

LGTM!