fix: update README Claude badge to Sonnet 4.6 (#2)

The README shield badge incorrectly displayed 'Claude Opus 4.6'.
The base agent default model (base_agent.py) is claude-sonnet-4-6.
Orchestrator still uses Opus for extended thinking — that is intentional
and documented in the architecture table below the badge.

Closes #1

Co-authored-by: Venkata Anil Kumar <VenkataAnilKumar@users.noreply.github.com>

Author: VenkataAnilKumar

README.md

@@ -13,7 +13,7 @@
 [![License: MIT](https://img.shields.io/badge/License-MIT-6366f1.svg?style=for-the-badge)](LICENSE)
 [![Python](https://img.shields.io/badge/Python-3.12-3776AB?style=for-the-badge&logo=python&logoColor=white)](https://python.org)
 [![Next.js](https://img.shields.io/badge/Next.js-15-black?style=for-the-badge&logo=next.js)](https://nextjs.org)
-[![Claude](https://img.shields.io/badge/Claude-Opus%204.6-D97706?style=for-the-badge&logo=anthropic&logoColor=white)](https://anthropic.com)
+[![Claude](https://img.shields.io/badge/Claude-Sonnet%204.6-D97706?style=for-the-badge&logo=anthropic&logoColor=white)](https://anthropic.com)
 [![FastAPI](https://img.shields.io/badge/FastAPI-0.115-009688?style=for-the-badge&logo=fastapi&logoColor=white)](https://fastapi.tiangolo.com)
 [![AWS Lambda](https://img.shields.io/badge/AWS-Lambda-FF9900?style=for-the-badge&logo=amazonaws&logoColor=white)](https://aws.amazon.com/lambda)
 [![CI](https://img.shields.io/github/actions/workflow/status/venkataanilkumar/launchiq/pr.yml?style=for-the-badge&label=CI&logo=githubactions&logoColor=white)](https://github.com/venkataanilkumar/launchiq/actions)