feat(policies): predefined compliance packs — CIS, HIPAA, PCI, NIST and more, out of the box

Ship thousands of predefined checks grouped by compliance framework, so tirith --pack cis -input-path plan.json covers a benchmark without the user writing anything. Terraform first, then
the other document kinds (CloudFormation, ARM, Kubernetes).

Source. A large verified translation set already exists internally (~2,700 policies translated
from public check libraries, each verified to pass a compliant and fail a violating document), and
the upstream checks carry compliance-framework tags — so framework packs are largely a regrouping
of that set, not new authoring. CIS ships first (the richest and best-structured tag set); PCI and
NIST follow; HIPAA and GDPR need an explicit mapping pass, since upstream tagging is sparser there.

Mechanics. Delivered through the pack manifest ("policy packs" issue) with meta.compliance
tags and meta.severity so --fail-on-severity gates them; deduplicated by
(resource type, attribute path) across source libraries (see the interoperability-packs issue);
coverage claims exclude never-firing stubs — a framework pack must state how many of the
benchmark's requirements it actually gates, not how many rows it contains.

Acceptance. tirith --pack cis -input-path plan.json runs a CIS pack end to end with per-policy
framework/severity metadata in every output format; each pack publishes an honest coverage
statement (requirements gated / requirements total); tirith test fixtures prove a sample of each
pack fires.

Start with the pack manifest and the related policy-packs and interoperability-packs work, then inspect the existing Terraform policy set and compliance-framework tags. Run the tirith --pack cis -input-path plan.json flow and tirith test fixtures. Done means CIS works end to end with framework/severity metadata, an honest coverage statement, and sample fixtures that fire.