feat: add GPU-specific fields to marketplace offers and create dedicated GPU marketplace router

- Add GPU fields (model, memory, count, CUDA version, price, region) to MarketplaceOffer model
- Create new marketplace_gpu router for GPU-specific operations
- Update offer sync to populate GPU fields from miner capabilities
- Move GPU attributes from generic attributes dict to dedicated fields
- Update MarketplaceOfferView schema with GPU fields
- Expand CLI README with comprehensive documentation and

apps/coordinator-api/src/app/services/marketplace.py

@@ -100,4 +100,10 @@ class MarketplaceService:
             sla=offer.sla,
             status=offer.status.value,
             created_at=offer.created_at,
+            gpu_model=offer.gpu_model,
+            gpu_memory_gb=offer.gpu_memory_gb,
+            gpu_count=offer.gpu_count,
+            cuda_version=offer.cuda_version,
+            price_per_hour=offer.price_per_hour,
+            region=offer.region,
         )