Add structured error logging to Lambda MCP server functions

[longwind48]

Problem

All Lambda MCP server functions use generic exception handling that returns plain error strings without context:

except Exception as e:
    return {"error": str(e)}

This makes debugging difficult in production — no stack traces, no request context, and no error classification in CloudWatch Logs.

Affected files:

• src/lambda/mcp_servers/cost_explorer/lambda_function.py
• src/lambda/mcp_servers/athena/lambda_function.py
• src/lambda/mcp_servers/cur_analyst/lambda_function.py

Expected Behavior

Each Lambda handler should log structured errors with:

• Handler/tool name that failed
• Input parameters (sanitized)
• Full stack trace via exc_info=True
• Use Python's logging module configured at module level

Example

import logging

logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)

def some_handler(event):
    tool_name = event.get("tool_name", "unknown")
    try:
        # ... handler logic
    except Exception as e:
        logger.error("Error in handler %s", tool_name, exc_info=True)
        return {"error": str(e)}

Scope

• Add logging import and logger setup to each affected Lambda
• Wrap existing except blocks with structured logging
• Do not change the return format — keep {"error": str(e)} for backward compatibility