Add TaffyJS website documentation

[hyfdev]

What changed

• Add a default-theme VitePress site and landing page for the TaffyJS package family.
• Add a homepage code-to-layout example whose displayed JavaScript runs through the real @taffyjs/wasm package and draws the rectangles returned by getLayout.
• Add a Guide and Essentials section that teach the layout model through CSS concepts, runnable examples, and a focused explanation of application-owned text and image measurement.
• Add an @taffyjs/node reference covering runtime support, topology, styles and context, computation, layout results, public value helpers, and errors.
• Add an @taffyjs/wasm package page covering supported environments, loading, bundling, and its observable differences from the native package.
• Run the Getting Started width example in the browser through the real @taffyjs/wasm package while keeping the Node example as the canonical code path.
• Build the website from the Wasm verification graph so the interactive examples and package cannot drift apart.
• Record the website information architecture and documentation ownership in the repository's decision documents.

Scope

This PR documents the current @taffyjs/node and @taffyjs/wasm APIs. It does not add empty pages for the future @taffyjs/yoga package, deployment configuration, or a release workflow. The packages remain private and unpublished.

Checks

• vp install --frozen-lockfile
• vp run ready
• vp run check:codegen
• vp run check:wasm
• Desktop, dark-mode, and 390px browser checks for both interactive Wasm examples, navigation, responsive diagrams, keyboard operation, console errors, and failed-Wasm loading states

[Copilot]

Pull request overview

This PR adds a new VitePress documentation site under apps/website to document the current TaffyJS package family (@taffyjs/node and @taffyjs/wasm), including interactive browser examples that run against the real @taffyjs/wasm package and build integration so the docs and Wasm verification graph stay aligned.

Changes:

• Introduces the @taffyjs/website VitePress app with Guide/Essentials content, per-package reference pages, and interactive demos.
• Wires website build/dev into the root Vite+ task graph and adds apps/* to the pnpm workspace with VitePress dependencies pinned via catalog.
• Adds/updates Project Context Records and READMEs to reflect documentation ownership and structure.

Reviewed changes

Copilot reviewed 32 out of 36 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
vite.config.ts	Adds build:website / dev:website tasks and runs the website build as part of check:wasm.
README.md	Links repo README to the new website docs entry points.
pnpm-workspace.yaml	Adds apps/* to the workspace and adds vitepress to the catalog.
pnpm-lock.yaml	Locks the new apps/website importer and VitePress/Vue dependency graph.
packages/taffyjs-node/README.md	Replaces long-form README content with install + links into the website reference.
apps/website/package.json	Defines the private VitePress app package and scripts.
apps/website/index.md	Adds the VitePress home/landing page and embeds the code-to-layout showcase.
apps/website/examples/home-layout.js	Provides the real runnable Wasm-backed layout example used by the home page.
apps/website/.vitepress/config.ts	Defines VitePress nav + sidebar structure for Guide/Node/Wasm sections.
apps/website/.vitepress/components/LayoutWidthDemo.vue	Implements the interactive Getting Started width demo using @taffyjs/wasm.
apps/website/.vitepress/components/HomeLayoutShowcase.vue	Implements the landing-page code-to-rectangles showcase and visualization.
apps/website/guide/index.md	Adds the Guide introduction and product framing.
apps/website/guide/getting-started.md	Adds Getting Started content plus an in-page interactive Wasm demo.
apps/website/guide/tree-compute-read.md	Adds an Essentials page explaining the core lifecycle and concepts.
apps/website/guide/styles-and-values.md	Adds an Essentials page explaining defaults, value helpers, and output snapshots.
apps/website/guide/block.md	Adds a Block-layout Essentials page with examples.
apps/website/guide/flexbox.md	Adds a Flexbox Essentials page with examples.
apps/website/guide/grid.md	Adds a Grid Essentials page with examples.
apps/website/guide/measuring-content.md	Adds the measurement Essentials page (text/images boundary + callback model).
apps/website/guide/getting-started-layout-model.svg	Adds the “browser vs TaffyJS layout pipeline” diagram.
apps/website/guide/measuring-text-and-images.svg	Adds the measurement flow diagram.
apps/website/node/index.md	Adds the @taffyjs/node overview page and section entry.
apps/website/node/nodes-and-topology.md	Adds the node/topology reference documentation.
apps/website/node/styles-and-context.md	Adds the styles/context reference documentation.
apps/website/node/computing-layout.md	Adds the compute/dirty/rounding/measurement reference documentation.
apps/website/node/layout-results.md	Adds the layout/detailed-grid output reference documentation.
apps/website/node/style.md	Adds the grouped StyleInput/Style field documentation.
apps/website/node/value-helpers.md	Documents numeric families and tagged value helper APIs.
apps/website/node/errors.md	Documents stable error codes and failure guarantees.
apps/website/wasm/index.md	Adds the @taffyjs/wasm overview/setup page and differences from native.
.gitignore	Ignores VitePress cache and build output directories.
.agents/docs/README.md	Adds the website PCR to the context record index.
.agents/docs/website.md	Records website information architecture and content ownership.
.agents/docs/technology-stack.md	Records the website build/tooling decisions and CI placement.
.agents/docs/intent.md	Refines intent wording and package-family direction statements.
.agents/docs/architecture.md	Updates the architecture PCR (but contains an inconsistency noted in review).

Files not reviewed (1)

• pnpm-lock.yaml: Generated file

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