feat(compliance): list undeclared features after validation

[grdsdev]

Summary

• Adds findMissingFeatureIds to compliance.ts — returns feature IDs in the canonical spec that are absent from an SDK's compliance file, sorted alphabetically.
• compliance-cli.ts (the validate-compliance script) now prints these missing IDs to stdout after a successful validation, grouped under a count line.
• Missing features continue to default to not_implemented; the exit code is unchanged — this is purely informational output.

Example output

OK — compliance file is valid.

47 feature(s) not declared (treated as not_implemented):
  - auth.mfa.enroll
  - auth.mfa.unenroll
  - storage.buckets.list
  ...

Test plan

• npm test passes (4 new tests added for findMissingFeatureIds)
• Validate against a real compliance file that omits some features and confirm the list appears
• Validate against a complete compliance file and confirm no list is printed