[Issue 20] Make bedrock model ID configurable

[deeheber]

🔧 Make Bedrock Model ID Configurable

Summary

Added environment variable configuration for Bedrock model ID to allow runtime model selection without code changes.

Changes Made

• ✅ Added BEDROCK_MODEL_ID environment variable support
• ✅ Created get_model_id() function with fallback to default model
• ✅ Updated agent initialization to use configurable model ID
• ✅ Added logging to show which model is being used
• ✅ Added fallback default model when no model provided

Configuration

Environment Variable: BEDROCK_MODEL_ID
Default: us.anthropic.claude-sonnet-4-5-20250929-v1:0

Local Development (.env file):

BEDROCK_MODEL_ID=us.anthropic.claude-3-5-sonnet-20241022-v2:0

fixes #20