Add Design mutations to the Workspace assistant

The Workspace assistant now supports creating and applying bounded operations to one exact Design, archiving or deleting it, managing comments and collaborators, creating or restoring versions, and creating, updating, or merging Branches. It can also publish or update Design Libraries, disable an enabled Library, and create a public prototype share for an exact flow. Consequential changes and public sharing require explicit confirmation in the current message. Design snapshots, operation payloads, manifests, and share tokens are not returned; successful writes return durable server-issued results and links.