Define standalone paginated export architecture

[JSv4]

Summary

• defines the single-renderer architecture for finalized offline paginated HTML and selectable PDF
• keeps conversion, pagination, materialization, PageMap, and reporting authoritative in the browser/WASM surface
• adds a Node-only @docxodus/export boundary with a closed public asset graph, deterministic Chromium policy, byte/path APIs, CLI, and framed .NET host
• defines truthful runtime/font attestations, readiness, resource limits, revision/comment profiles, failure reports, and PDF fidelity gates
• specifies the explicit grouped RenderBatchAsync seam that the existing draft delivery PR Orchestrate verified delivery bundles #499 will consume
• maps [HTML] Materialize standalone paginated HTML #438–[PDF] Add explicit revision and comment rendering profiles #444 and Footnote continuation stops at the paragraph: an oversized note paragraph is clipped, not split #489 into a cohesive dependency order and retains Add deterministic OOXML package manifests #493 as the authoritative package-preflight contract

Why

Epic #434 is the remaining production-rendering dependency for #465. This decision prevents the child issues from introducing a second converter, hidden cross-artifact caching, incomplete offline HTML, or unverifiable PDF output.

Validation

• independently audited against the current browser/pagination implementation
• independently audited against Chromium PDF behavior and delivery-report requirements
• independently audited against live [Epic] Standalone paginated HTML and PDF export #434 child issues and the current Orchestrate verified delivery bundles #499 renderer seam
• git diff --cached --check
• documentation-only change; no runtime tests required

Closes #437