docs: add status badges to README

[pmady]

Summary

Add status badges to the top of README.md for quick project health visibility.

Badges to add

• CI status (GitHub Actions)
• Go Report Card
• Go Reference (pkg.go.dev)
• License (Apache 2.0)
• GitHub stars
• GitHub release (latest)

Example format

[![CI](https://github.com/pmady/gpu-mcp-server/actions/workflows/ci.yml/badge.svg)](https://github.com/pmady/gpu-mcp-server/actions/workflows/ci.yml)
[![Go Report Card](https://goreportcard.com/badge/github.com/pmady/gpu-mcp-server)](https://goreportcard.com/report/github.com/pmady/gpu-mcp-server)
[![Go Reference](https://pkg.go.dev/badge/github.com/pmady/gpu-mcp-server.svg)](https://pkg.go.dev/github.com/pmady/gpu-mcp-server)

Acceptance criteria

• Badges added after the # gpu-mcp-server heading
• All badge links work
• Badge row is on a single line (no line breaks between badges)

Difficulty: Beginner — markdown only