Add CI/lint checks to enforce docs, types, and API stability

[sagpatil]

Motivation: Keep quality high as types and docs evolve by adding CI checks and automation guardrails.

Proposed approach:

• Add CI checks for TypeScript typechecking of migrated modules, JSDoc presence on public exports, and API diff checks for breaking changes.
• Document a policy for handling breaking changes and required reviewer checks.

Acceptance criteria:

• CI runs the new checks on PRs.
• A documented policy for breaking changes is available.