chore(examples): bump the starter to @workflowbuilder/sdk 3.0.0

[librowski]

Summary

The StackBlitz starter in examples/workflow-builder-starter still pinned @workflowbuilder/sdk 2.2.0. This bumps it to 3.0.0 so the "Open in StackBlitz" links in the README show the current SDK and Design System 2.0.

The starter uses none of the surfaces that 3.0 removed (no @synergycodes/overflow-ui imports, no --ax-* tokens, no ax-public-* classes), so only package.json and package-lock.json change.

Verification

• npm install and npm run build (tsc --noEmit and vite build) pass in examples/workflow-builder-starter.
• The dev server renders the three starter nodes with the 3.0 styles and logs no console errors or warnings.