Upgrade Python runtime from 3.12 to 3.13 (current GA)

[paulyuk]

Summary

Upgrade the Python MCP runtime from 3.12 to 3.13, which is the latest GA version supported by Azure Functions.

Current State

infra/main.bicep:

runtimeName: 'python'
runtimeVersion: '3.12'

Proposed Changes

infra/main.bicep:

runtimeName: 'python'
runtimeVersion: '3.13'  // Latest GA

Why This Change?

Python 3.13 is now the latest GA version supported by Azure Functions Flex Consumption plan.

Testing Checklist

• pip install -r requirements.txt succeeds
• func start discovers all MCP tools
• azd up deploys successfully
• MCP tools respond correctly via HTTP transport

Reference

• Azure Functions Python Support