Migrate consumers to @workflowbuilder/ui (2/3: consumers)

[librowski]

Part 2 of 3. Stacked on #41 (base branch librowski/ui-package) - review/merge that first. This PR's diff is only the consumer migration.

Summary

Switches sdk / demo / ai-studio off the published @synergycodes/overflow-ui@1.0.0-beta.27 (MUI) onto the in-repo @workflowbuilder/ui (Base UI) added in Part 1, and fixes the resulting API breaks.

Changes

• 75 imports @synergycodes/overflow-ui → @workflowbuilder/ui; dependency → workspace:*; @base-ui/react added to sdk/demo/ai-studio.
• Removed the LOCAL_OVERFLOW_UI vite aliases, the overflow-ui-css alias, and the dev:local script. SDK index.css now pulls @workflowbuilder/ui/{tokens,index}.css.
• Fixed the real Base UI API breaks: Switch.onChange(checked, event) and DatePicker date-fns valueFormat. Menu / Select / IconSwitch / Tooltip were already compatible.
• Renamed in-source references (sdk comments/JSDoc) and the docs code-example imports to @workflowbuilder/ui.
• Changeset for @workflowbuilder/sdk included.

Verification

• pnpm install clean; build, build:lib, build:ai-studio, build:docs green; typecheck, lint, test (sdk 184 + execution-core 78) green.
• Rendered demo + ai-studio in a browser: components styled (layer order, switches, modal backdrop transition, datepicker, select). The base-ui 1.4.1 pin (Part 1) is what keeps the modal backdrop fade working - 1.6.0 regressed it.
• Nothing resolves @synergycodes/overflow-ui from npm or the old local dist path.

[librowski]

Superseded by the rebranched series (no librowski/ prefix): #44 (packages), #45 (consumers), #46 (docs). Closed automatically when the head branch was renamed.