Tasks — crypto-cipher-spec-conformance

Add **Verified by:** line to every ### Requirement: block in openspec/specs/crypto-cipher/spec.md.
Add tests/spec-conformance.test.ts pinning structural scenarios.
Confirm bun scripts/openspec-conformance.ts @suaveplan/crypto-cipher exits 0.
Confirm bunx turbo lint typecheck test --filter=@suaveplan/crypto-cipher is green.
Confirm bunx turbo test:coverage --filter=@suaveplan/crypto-cipher reports 100/100/100/100.