Adopt HIG tokens, typography and accessible states in Chart docs

[joeblau]

Chart docs used a copied token palette, separate heading font and duplicate install-copy handling. This adopts HIG 0.1.0 candidate presentation for the docs shell and embedded chart while preserving the SDK engine, API examples, static hosting paths and demo interactions.

• Pin the approved plain CSS distribution and manifest to bloxwap/hig@1a776b9326c6ba03702894943b3edbfd178c4b40, retaining license and SHA-256 provenance. The candidate is unpublished; no npm publication or new runtime dependency is involved.
• Derive Fumadocs semantics, type/spacing/geometry/density/motion and sRGB chart theme from that manifest. Use Bloxwap Sans for headings; remove the unused Space Grotesk face and copied palette.
• Share copy handling, suppress pending duplicate activation, announce results, display recoverable errors, and expose search failures. Provide chart text/loading descriptions, dark docs embedding and reduced-motion/coarse-pointer presentation.
• Gate production browser behavior and scoped drift checks in docs CI. Record ownership, dated exceptions, upgrade and atomic rollback instructions.

Relates to bloxwap/hig#33, bloxwap/hig#34 and bloxwap/hig#36; documents bloxwap/hig#35's native boundary. No upstream issue is closed or declared complete by this repo-only work.

Validation on Linux, Node 24.21.0, Next 16.3.6, Chrome 154.0.8037.97:

• npm ci: passed.
• npm run lint: passed (137 icons, pinned hashes, generated adapter and scoped copied-palette/obsolete-import checks).
• npm run typecheck: passed (SDK tsc, Next type generation, docs tsc).
• npm run coverage: 1,869 passed, 0 failed; 100% line/branch/function across 138 files; includes production SDK build/icons/WASM.
• NEXT_PUBLIC_BASE_PATH=/chart NEXT_PUBLIC_SITE_URL=https://bloxwap.github.io npm run docs:build and npm run docs:check: passed. Static export verifies 30 HTML pages, 1,530 local links/assets and 25 social cards.
• npm run docs:test: passed. Real Chromium verifies keyboard install tabs, pending/success/denied clipboard behavior and live regions, HIG fonts/palette/reduced motion, offline WebGL2 demo (500 candles, no duplicate/missing buckets, bid/ask depth), settings/Escape/pointer/wheel, search results/dismissal, RTL/200% text, 48px touch-emulated copy target and mobile navigation. Shell-control checks isolate the iframe; the distinctive demo is exercised separately.

Proof is committed in docs/hig-adoption: before/after 1440×1000 screenshots, mobile capture, observed browser JSON, validation record and reproducible size report. Baseline: e08198bcff27451defeca238e832d4be54be1896, same toolchain and /chart export settings. Total uncompressed emitted CSS −893 bytes; JS −11,008 bytes; fonts −116,056 bytes. These totals are not per-route or transferred bundle claims. Playground captures use the same offline synthetic market; live timestamps and interaction state are not a pixel-diff assertion.

Remaining evidence is explicit: Linux browser/touch emulation cannot certify physical touch/mobile chart gestures, iOS hardware, VoiceOver/TalkBack, tactile feedback or wide-gamut displays. No effects/adapters or preference changes were introduced. Product/native migrations and the other four SDK docs repos remain owned elsewhere. HIG maintainers must copy this PR/version/evidence into the canonical org matrix; stable HIG publication and org-wide completion remain upstream. Standalone SDK themes remain host-configurable; the dated Chart exception and decorative OG brand-spectrum exception are in the report (review 2026-11-13).

Rollback: revert this PR atomically (baseline CSS/fonts/controls); no storage/schema migration. No releases, tags, npm publishes or manual production deployment actions are part of this PR.