Documentation cleanup: Remove X-Ray, Gateway, and unused config from observability sample

## Overview
This branch contains documentation and configuration cleanup for the Simple Dual Observability sample.

## Changes from main

### Removed
- All X-Ray references (replaced with CloudWatch Logs focus)
- AgentCore Gateway component from architecture (direct MCP tool usage)
- Unused `config/otel_config.yaml` file
- Redundant CloudWatch log sample files

### Updated
- Architecture diagrams and descriptions
- Real OTEL-rt-logs examples from actual agent execution
- Real Braintrust log entry examples
- AWS credential configuration documentation
- Troubleshooting guide for tool execution
- Development guide file structure

### Result
Cleaner, more accurate documentation focused on what actually works:
- CloudWatch Logs for runtime visibility
- MCP tools for agent functionality
- Braintrust integration (optional)
- Strands telemetry library for automatic OTEL configuration

## Branch
`observability-docs-improvements`

Compare: https://github.com/awslabs/amazon-bedrock-agentcore-samples/compare/main...aarora79:amazon-bedrock-agentcore-samples:observability-docs-improvements