docs: tighten webgpu public claims

[shtse8]

Summary

• Tighten README and docs wording around WebGPU compatibility, runtime performance, package size, and consumer install claims.
• Replace absolute or unsupported claims with measured-boundary language: native Rust/wgpu backend, documented package surface, platform package sizes, adapter/backend/workload metadata for benchmarks.
• Remove test-log overclaims and refresh tracked VitePress dist, including ADR/spec pages.
• Fix Doctrine adapter enum drift while keeping the vendor-neutral GroundAtlas manifest adopted.

Validation

• bun install --frozen-lockfile
• bun test
• bun run build
• bun run docs:build
• bun run release:readback
• /Users/kyle/.cache/codex-runtimes/codex-primary-runtime/dependencies/node/bin/node --test test/project-control.node-test.mjs
• python3 /Users/kyle/.doctrine/scripts/project-control-plane-audit.py --local . --fail-on-drift --json
• git diff --check
• pnpm dlx groundatlas@0.1.2 update --out .groundatlas-pilot
• pnpm dlx groundatlas@0.1.2 audit --out .groundatlas-pilot
• pnpm dlx groundatlas@0.1.2 manifest --out .groundatlas-pilot --json
• pnpm dlx groundatlas@0.1.2 fleet . --out .groundatlas-pilot --require-atlas --strict --json

Notes

• This does not publish a new package version; npm readback remains verified for @sylphx/webgpu@1.0.4 and all six platform packages.
• Python/NumPy/PyTorch parity claims remain owned by consumers such as tsnum/axon, not by the backend substrate alone.