📋 Marketplace Endpoints:
• GET /marketplace/listings - List all active marketplace items
• POST /marketplace/create - Create new marketplace listing
• Demo listings for GPU and compute resources
• In-memory storage with active status filtering
🤖 AI Services Endpoints:
• POST /ai/submit - Submit AI jobs with payment
• GET /ai/stats - AI service statistics and revenue tracking
• Support for text, image, and training job types
