Add delivery protection operator docs, fix marketplace operator signature

[mintlify]

Summary

• Documents the new deployDeliveryProtectionOperator() and previewDeliveryProtectionOperator() presets from backtrackco/x402r-sdk@42fa2ad
• Fixes deployMarketplaceOperator() and previewMarketplaceOperator() signatures to match the actual API (chainId in options object instead of separate networkId string parameter)
• Updates MarketplaceOperatorDeployment return type to match source (adds refundRequestAddress, refundRequestEvidenceAddress, operatorConfig, corrects summary field names)
• Adds a preset comparison table to help users choose between marketplace and delivery protection operators
• Applies sentence-case headings per CLAUDE.md style guide

Changed files

• sdk/deploy-operator.mdx — New delivery protection section, corrected marketplace operator signatures and return types
• sdk/examples.mdx — Updated code snippet with correct signature, added delivery protection example