Add BedrockClient using langchain-aws ChatBedrockConverse, enabling
TradingAgents to use Bedrock-hosted models (Claude, Kimi, Qwen, GLM, etc.)
via IAM Role authentication without API keys.
Usage:
config['llm_provider'] = 'bedrock'
config['deep_think_llm'] = 'us.anthropic.claude-sonnet-4-5-20251001-v1:0'
config['quick_think_llm'] = 'us.amazon.nova-lite-v1:0'
Requires: langchain-aws>=0.2.0