Move overflow-ui in-repo as @workflowbuilder/ui + UI Library docs

[librowski]

Summary

Moves the overflow-ui component library (the Base UI rewrite) into this monorepo as the publishable @workflowbuilder/ui package, switches all consumers off the published @synergycodes/overflow-ui@1.0.0-beta.27 (MUI) onto it, and builds a full UI Library documentation section (page-per-component, twin to the Overflow UI docs) with source-generated API tables and a Design Tokens pipeline page.

Decisions taken with the maintainer: rename to @workflowbuilder/ui (+ @workflowbuilder/ui-tokens), keep it publishable to npm, consume built dist via workspace:*.

What's in here

Package move

• packages/ui (@workflowbuilder/ui) + packages/tokens (@workflowbuilder/ui-tokens) brought in from overflow-ui@base-ui-migration, preserving the multi-entry build, the CSS @layer contract (ui.base/ui.component), and combine-css-bundle. Dropped decision-logs, the overflow-ui.js back-compat shim, dead deps, and the preview app.
• Aligned with root tooling (eslint/tsconfig extend root), deps onto the catalog:, React 18→19, @base-ui/react added to the catalog.

Consumers (sdk / demo / ai-studio)

• 75 imports @synergycodes/overflow-ui → @workflowbuilder/ui; workspace:*; @base-ui/react added; removed the LOCAL_OVERFLOW_UI vite aliases + overflow-ui-css alias + dev:local; SDK index.css switched to @workflowbuilder/ui/{tokens,index}.css.
• Fixed the real Base UI API breaks against the new surface (Switch.onChange(checked, event); DatePicker date-fns valueFormat). Menu/Select/IconSwitch/Tooltip were already compatible.
• @base-ui/react pinned to 1.4.1 (the version the library was validated against) - 1.6.0 changed Dialog transitions and broke the modal backdrop fade.

Build

• dist builds on pnpm install via prepare (topological: tokens → ui); build:lib chains tokens → ui → sdk.

Docs (apps/docs, Starlight)

• New UI Library section: Overview, Design tokens page, UI Components (18 pages) and Diagram Components (5 pages) - one page per component with a live interactive example (React island), usage, props, and CSS variables.
• Props & CSS-variable tables are generated from source (scripts/generate-ui-api.mjs): TypeDoc extracts per-component props (type/required/default/description) from the library's prop types; CSS variables are extracted from the component stylesheets. Rendered inline via PropsTable / CssVariablesTable Astro components - no hand-maintained tables.
• Design Tokens page documents the tokens.json (Figma) → style-dictionary → --ax-* CSS pipeline, theming, customization, and the known "missing token" gaps.

Verification

• pnpm install clean; build, build:lib, build:docs, build:ai-studio green; pnpm typecheck, pnpm lint, pnpm test (sdk 184 + execution-core 78) green.
• Rendered demo + ai-studio + docs in a browser: components styled (layer order, switches, modal backdrop transition, datepicker, select), docs pages live + interactive, themed with Starlight.
• Nothing resolves @synergycodes/overflow-ui from npm or the old local dist path.

Notes for reviewer

• pnpm check is red only on pre-existing astro check errors in apps/docs head.astro / sidebar.astro (untouched here; reproduces with this branch's changes stashed). All other gates pass.
• A changeset is included for @workflowbuilder/sdk (consumes the in-repo UI). @workflowbuilder/ui is now a second publishable package, so the release tag scheme (v*) needs migrating to scoped tags before publishing it - flagged in CLAUDE.md / packages/sdk/RELEASE.md (maintainer, out of scope here).
• Added missing lint-staged.config.mjs to packages/ui and packages/tokens (they were never committed through the hook before).

Out of scope

No npm publish; no release-workflow / tag-scheme migration; the "Overflow" product upsell card (overflow-card.astro) is left as-is (it advertises the commercial product, not the vendored library).

[librowski]

Split into #41 (package + consumers) and #42 (UI Library docs, stacked on #41) for easier review.