Add GitHub Actions workflow for automated Docker builds

[Copilot]

Automates Docker image builds and publishes to Docker Hub as cloud-server:latest on main branch pushes, with semantic versioning support for tagged releases.

Workflow Configuration

• Triggers: Push to main (→ latest tag), version tags (→ semver tags), PRs (build-only validation)
• Image name: <username>/cloud-server
• Tag strategy:
  • latest on main branch
  • 1.0.0, 1.0 on version tag v1.0.0
• Build optimization: Docker Buildx with GitHub Actions cache
• Security: Minimal GITHUB_TOKEN permissions (contents:read, packages:write)

Required Configuration

Publishing controlled by repository variable DOCKER_ENABLED=true with secrets:

• DOCKER_USERNAME: Docker Hub username
• DOCKER_PASSWORD: Docker Hub access token

Image name falls back to github.repository_owner when DOCKER_USERNAME unset, allowing builds without credentials.

Documentation

README updated with Docker Hub usage instructions and CI/CD documentation.

Original prompt

给项目添加github action自动docker打包，镜像为cloud-server，记得打latest

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[Copilot]

Pull request overview

This pull request adds automated Docker image builds and publishing to Docker Hub using GitHub Actions. The workflow is configured to build the cloud-server Docker image and publish it as <username>/cloud-server with appropriate tags based on the trigger event.

Changes:

• Added .github/workflows/docker.yml workflow that builds and publishes Docker images on pushes to main and version tags
• Updated README.md with Docker Hub usage instructions and CI/CD documentation explaining the workflow configuration

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

File	Description
.github/workflows/docker.yml	New GitHub Actions workflow for automated Docker builds with Docker Hub publishing, semantic versioning support, and build-only validation for PRs
README.md	Added documentation for pulling pre-built images from Docker Hub and CI/CD workflow configuration details

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[Copilot]

The statement "The workflow will build the Docker image on every push" is misleading. According to the workflow configuration, it only runs on pushes to the main branch or version tags (e.g., v1.0.0), not on every push to every branch. Consider rephrasing to: "The workflow will build the Docker image on every push to the main branch and on version tag pushes".

Suggested change

	The workflow will build the Docker image on every push and only push to Docker Hub if the `DOCKER_ENABLED` variable is set to `true`.
	The workflow will build the Docker image on every push to the `main` branch and on version tag pushes, and will only push to Docker Hub if the `DOCKER_ENABLED` variable is set to `true`.

[Copilot]

The documentation doesn't mention that the workflow also runs on pull requests targeting the main branch for build validation (without pushing to Docker Hub). Consider adding this information to the "Trigger" section: "- Pull requests to main (build-only validation without pushing to Docker Hub)".

Suggested change

	- **Trigger**: Automatically runs on push to `main` branch and on version tags (e.g., `v1.0.0`)
	- **Trigger**: Automatically runs on push to `main` branch, on pull requests targeting `main` (build-only validation without pushing to Docker Hub), and on version tags (e.g., `v1.0.0`)

[Copilot]

The image name documentation is incomplete. The actual Docker image name is <username>/cloud-server (where username is from DOCKER_USERNAME secret or github.repository_owner), not just cloud-server. This should be updated to match the actual naming convention used in the workflow (line 41 of docker.yml).

Suggested change

	- **Image name**: `cloud-server`
	- **Image name**: `<username>/cloud-server` (where `<username>` is your Docker Hub username or the GitHub repository owner)