feat(context-delivery): implement governed consumer boundary

[adamshen1007]

Summary

• add strict provider-neutral Consumer, Delivery Request, Policy Decision, freshness, replay, envelope, acknowledgment, receipt, and evidence contracts
• implement fail-closed governed Context Package delivery with authoritative verification, historical registry-prefix recovery, capability matching, and bounded idempotency
• add 40 executable evaluation scenarios plus comprehensive integrity, privacy, tamper, replay, and regression coverage
• update architecture and package documentation

Verification

• pnpm format:check
• pnpm lint
• pnpm build
• pnpm typecheck
• pnpm test — 506 tests passed
• git diff --check
• independent whole-branch review — CLEAN

Scope

No LLM/provider invocation, agents, Hermes, MCP, persistence, semantic retrieval, embeddings, vector database, ranking, knowledge graph, external integrations, or UI were introduced.