feat(phase-27): add checklist item acknowledgments and acknowledgment notes

[xiwuqi]

Summary

This direct-to-main PR completes Phase 27: Cross-Run Audit Catalog Checklist Item Acknowledgments and Acknowledgment Notes.

Phase 27 has already passed stage review.
This branch is a direct branch, not a stacked branch.

It adds:

• a shared audit-catalog checklist-item-acknowledgment contract
• acknowledge / list-acknowledged / inspect-acknowledgment / clear-acknowledgment / apply paths through existing SDK / API / CLI / web seams
• inline-originated and queued-originated integration coverage
• Phase 27 docs, ADR, guide, and roadmap status sync

Scope boundaries

This PR does not change replay or approval source of truth.
It does not add full observability backend integration, productized dashboards, broad analytics or search products, fine-grained RBAC, multi-tenant access, approval products, workflow gating, artifact vault behavior, copied artifact persistence, attachment-upload products, threaded collaboration, broader checklist orchestration, broader review workflow engines, broader SaaS concerns, or any Phase 28 work.
Provider-specific payloads, copied artifacts, and workflow-state snapshots do not enter the shared contract.

README is not a blocker for this PR, so this PR intentionally does not expand scope into README updates.
The Current Status drift at README.md line 19 remains a separate non-blocking docs sync item.

Validation

• changed-files Biome check passed
• git diff --check passed
• pnpm typecheck passed
• pnpm test passed
• pnpm test:integration passed
• pnpm build passed
• repo-wide pnpm lint in the current Windows worktree still reports CRLF / formatter drift outside the Phase 27 diff
• clean LF clone repo-wide pnpm lint passed