Add README badges for cross-platform CI coverage

[Copilot]

The README did not clearly communicate that CI validates builds across macOS, Linux, and Windows. This update makes platform coverage visible at a glance from the repository landing page.

• What changed

  • Added a live GitHub Actions badge for the build-and-test workflow on main.
  • Added explicit platform badges for Linux (ubuntu-latest), macOS (macos-latest), and Windows (windows-latest) to reflect matrix coverage.

• README update (snippet)

  [![Build and test](https://github.com/lab-core/dynamic-ips/actions/workflows/build-and-test.yml/badge.svg?branch=main)](https://github.com/lab-core/dynamic-ips/actions/workflows/build-and-test.yml)
  ![Linux](https://img.shields.io/badge/Linux-ubuntu--latest-informational)
  ![macOS](https://img.shields.io/badge/macOS-macos--latest-informational)
  ![Windows](https://img.shields.io/badge/Windows-windows--latest-informational)

[Copilot]

Pull request overview

This PR updates the repository landing page to clearly communicate that CI validates builds/tests across Linux, macOS, and Windows by adding a GitHub Actions workflow badge plus explicit OS/platform badges.

Changes:

• Added a GitHub Actions badge for the build-and-test.yml workflow on the main branch.
• Added static platform badges indicating the CI matrix OS coverage (ubuntu-latest, macos-latest, windows-latest).

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