fix(bedrock): improve AWS credential handling and add model definitions

- Change error to warning when AWS credentials are missing in environment
- Allow fallback to system configuration (aws config files or instance profiles)
- Remove hardcoded region and profile parameters in Bedrock client
- Add Claude 3.7 Sonnet and DeepSeek R1 model definitions for Bedrock
- Update config manager to properly handle Bedrock provider

.changeset/modern-cats-pick.md

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+---
+"task-master-ai": patch
+---
+
+Improves Amazon Bedrock support