Move Design System Sync From Claude Design to Artifacts #998

Part of TEDI-Design-System/general#253.

Claude Design is moving into Claude as Artifacts, and the standalone site closes on 14 December 2026. The TEDI design system was already migrated to an artifact, but our sync still uploads to the old standalone project, so the version Claude uses is out of date (19.0.0-rc.2).

Move the sync straight to Artifacts, without keeping the old flow alongside it:

• Sync publishes to the TEDI Design System artifact
• Drop the standalone project setup
• Bring the artifact up to the current release
• Update DESIGN.md, README.md and the sync notes