AWS Bedrock SDK Integration

A complete AWS SDK v3 integration for Bedrock Runtime has been added, including:

• Bedrock Runtime client with full middleware stack
• AWS Signature Version 4 (SigV4) request signing
• OAuth2 credential provider for AWS login flows
• ECS/EKS container credentials support
• Assume Role with MFA support
• 30+ Bedrock API command definitions (guardrails, inference profiles, model management)
• AWS STS client for credential operations
• EventStream marshalling for real-time bidirectional communication

This replaces the previous Bedrock integration approach with a more complete, standards-compliant AWS SDK implementation.