feat(domformat): port retained adapter techniques

[alowpoly]

Summary

• port the reusable retained-DOM techniques from the stable cssGraphics demos into DOMFORMAT's closed, validated codecs and runtime
• add sparse class variants, packed two-axis surface positions, verified paged playback/variant state, bounded residency, responsive presentation/profile timelines, parametric leaf layouts, profile-by-frame visibility, typed orbit input, compositor timing, rational cadence/catch-up, and host-selected retained bank handoff
• keep production, alternate viewer, N-version JavaScript, and Python readers aligned, including fail-closed resource, ordering, memory, cancellation, and atomic-publication checks
• migrate gallery source identity from the singleton sourceArtifact field to bounded artifacts[], and update all 295 affected canonical corpus documents
• code-split and Terser-minify the npm runtime while retaining stable public entry points and declarations

Why

DOMFORMAT previously represented only a narrow subset of the prepared state that the cssGraphics adapters already prove useful. That forced viewers to reimplement paging, responsive selection, cadence, sparse publication, input mapping, and retained-bank behavior outside the document contract. This PR moves those deterministic data/runtime mechanisms into DOMFORMAT while keeping product policy and Morph-owned behavior out.

The source review is pinned to cssGraphics revision bb2d0b030b9a5b15f2268d8221b57b56fb61be30. The compatibility proof covers the seven stable browser demos: 3D Pipes, ElectroPaint, Gears, Gravity Well, Maze, Menger, and Solitaire. Flowerbox is explicitly excluded because it is experimental. SM64's custom/Morph prepared-package path and random bank-selection policy remain outside DOMFORMAT.

The compatibility claim is deliberately mechanism-level: it does not claim exact source schedule lowering, producer equivalence, topology equivalence, or pixel parity.

Verification

• pnpm --filter @layoutit/polycss-domformat test:coverage
• pnpm --filter @layoutit/polycss-domformat test:release
• pnpm gallery:domformat:verify
• pnpm test
• pnpm build
• pnpm check:readmes
• pnpm test:scripts
• git diff --check

The installed-tarball browser proof exercises all seven stable demo contracts through the reference viewer, alternate viewer, and N-version reader, including their actual cadence classes and retained sink changes. Real-size ElectroPaint and Gravity Well state pages also pass the six-path responsiveness/atomicity trace: no observed long tasks and all measured main-thread tasks below 50 ms.

The deterministic release check produces a 98,057-byte tarball (365,000 bytes unpacked, 19 entries), 4,343 bytes below the 100 KiB packed-size ceiling.