feat: sync SDK with current worker ZIP contract and agentic retrieval API

[suguanYang]

Summary

Syncs the Node SDK with two server-side changes (same as Python SDK #23).

Issue #80 — Align ParseResult ZIP types with current worker output

• DocNav types — DocNavSection, DocNavResources, DocNavResourceItem for doc_nav.json (sections tree + resource summaries)
• Manifest HIERARCHY — exposed as HIERARCHY?: Record<string, unknown> (all-caps runtime key preserved since keysToCamel() doesn't transform it)
• documentTopSummary — parsed from chunk metadata on all chunk types
• Legacy deprecation — tableType, chunksSlim, hierarchy, tocHierarchies, kbCsv, hierarchyViewHtml marked @deprecated
• save() writes doc_nav.json when present

Issue #81 — Add agentic retrieval response fields

• useAgentic on RetrievalQueryParams
• answerText and referencedChunks on RetrievalQueryResponse
• All new fields optional for backward compatibility

Test plan

• All 243 existing + new tests pass (11 test files)
• doc_nav.json round-trips through parse + save
• HIERARCHY exposed from manifest
• documentTopSummary on text, image, and table chunks
• Parsing succeeds without chunks_slim.json or hierarchy.json
• useAgentic sent correctly; answerText / referencedChunks parsed
• Legacy response (no agentic fields) parses without error

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