Add Mayo Clinic & Siemens Digital Marketplace

   case study

  - Create new mayo-siemens-case-study.html showcasing global deployment via Siemens Digital Marketplace
  - Update mayo-case-study.html with enhanced styling and call-to-action
  - Add mayo-siemens-marketplace.jpg showing CAII Viewer integration
  - Document journey from institutional development to 10,000+ institution access

Author: zephyrie