GitHub Action: validate council-review JSONs against COUNCIL_REVIEW_TEMPLATE.json

[Aetherneum-linework]

Now that council/council.py exists and emits the same JSON schema as the reviews under cohort-phase-0/council-reviews/, a CI gate would catch malformed reviews before they hit main.

What to do:

• Add .github/workflows/validate-reviews.yml
• On every PR touching cohort-*/council-reviews/*.json: validate each changed JSON with jsonschema (Python) or ajv-cli
• Fail the check if any JSON deviates from the schema produced by council/council.py
• Bonus: extract a formal JSON Schema from the committed reviews and check it in

Success looks like: a malformed council JSON is caught at PR time, not after merge.