chore: add Docker containerization for local development and testing

[Pahari47]

What does it do?

Adds Docker containerization support for Hexo’s core repository to simplify local development, testing, and CI consistency.

Currently, Hexo requires manual Node.js setup (>=20.19.0). This PR introduces a standardized Docker environment allowing contributors to build, serve, and test Hexo inside an isolated container — reducing setup friction and ensuring consistent builds across systems.

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Solution

Introduced a minimal Dockerfile (based on Node 20 Alpine) and an optional docker-compose.yml for quick startup.
The image installs dependencies, builds the project, and can run either the development server or test suite.

Key Highlights:

• Uses official node:20-alpine base (aligns with Hexo 8+ requirements)
• Installs dependencies and builds Hexo inside container
• Exposes port 4000 for hexo server
• Optional volume mapping for live development with Docker Compose

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Changes Made

• Dockerfile: Added Node 20 Alpine image for reproducible environment
• docker-compose.yml: Added for quick setup and local testing

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Pull request tasks

• Add Dockerfile
• Add docker-compose.yml
• Update documentation
• Test container build and hexo server functionality
• Passed the CI test

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Testing

✅ Verified that Hexo builds and serves locally using Docker
✅ hexo generate and hexo server run successfully inside container
✅ Compatible with Node.js 20 and Alpine environment
✅ No impact on existing development workflow

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Example Usage

# Build Docker image
docker build -t hexo-dev .

# Serve site inside container
docker run -p 4000:4000 hexo-dev

# Or use Docker Compose for convenience
docker-compose up

[github-actions]

How to test

git clone -b new-feature https://github.com/Pahari47/hexo.git
cd hexo
npm install
npm test