Add GitHub Actions workflow for Docker image build and push

[Copilot]

No automated pipeline existed to build and publish the Docker image defined in the repo's Dockerfile.

Changes

• New workflow (.github/workflows/docker.yml): builds and pushes to ghcr.io/<owner>/<repo> on push to main, version tags (v*), or manual dispatch
• Multi-platform: builds linux/amd64 and linux/arm64 via QEMU + Buildx
• Tagging strategy: branch name, semver ({{version}}, {{major}}.{{minor}}), and short commit SHA via docker/metadata-action
• Caching: GitHub Actions cache (type=gha) for faster layer reuse
• Auth: uses built-in GITHUB_TOKEN with packages: write — no extra secrets required

- name: Build and push Docker image
  uses: docker/build-push-action@v6
  with:
    context: .
    platforms: linux/amd64,linux/arm64
    push: true
    tags: ${{ steps.meta.outputs.tags }}
    cache-from: type=gha
    cache-to: type=gha,mode=max

Pull the image after a successful run:

docker pull ghcr.io/luo923/cursor2api-go:main

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[Copilot]

Pull request overview

Adds an automated GitHub Actions pipeline to build and publish the repository’s Docker image to GitHub Container Registry (GHCR), enabling repeatable multi-arch image releases without manual steps.

Changes:

• Introduces a new workflow that builds and pushes images on pushes to main, version tags (v*), and manual dispatch.
• Uses QEMU + Buildx to publish multi-platform images (linux/amd64, linux/arm64).
• Implements consistent tagging/labeling via docker/metadata-action plus GitHub Actions cache for faster rebuilds.

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