feat: add PolyCSS Morph

[alowpoly]

Summary

• add @layoutit/polycss-morph 0.0.1 with strict prepared-model contracts, deterministic Node preparation, browser loading, and a retained PolyCSS mount
• support static-prepared, morph-regions, joint-skin, and prepared-playback through caller-driven sparse runtimes with no owned scheduler
• generate polygon-sized prepared alpha-atlas fallbacks with Node built-ins and render the SHA-256-verified bytes through retained object URLs
• harden package path confinement, resource budgets, glTF parsing, animation, deformation, skinning, springs, and atomic retained updates
• keep the release package-focused: no Morph example workspace, public demo routes, generated example artifacts, or product-specific adapters
• publish Morph through the existing all-packages workflow; package discovery now keeps every package version in lockstep
• enforce Morph coverage plus offline-tarball and registry-dependency package certification in the shared CI workflow
• delegate solid-triangle feature detection to the public PolyCSS renderer contract and certify both native and prepared-fallback mount branches

Verification

• pnpm test && pnpm build — 2,923 tests; all packages, examples, and the website build
• pnpm --filter @layoutit/polycss-morph test:coverage — 166 tests; 91.16% statements/lines, 83.02% branches, 97.73% functions
• pnpm --filter @layoutit/polycss-morph test:package
• pnpm --filter @layoutit/polycss-morph test:package:registry
• certified tarball: 91,625 bytes, 13 files, SHA-256 45286f644052da28ef2a3b66036e936ad991bc3cbb3a99cf439a3371c6351dd9

The CI certification exercises native and prepared fallback selection, but this PR does not claim a real-browser Chromium/Firefox/WebKit Playwright smoke.