Reduce redundancy; improve coverage of excluding .env.* files.

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run node update-readme.js and verified that README.md is up to date.

Description

Minor updates to the containerization .dockerignore example; to reduce redundancy and extend the .env file exclusions pattern to all .env.* files.

Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• Other (please specify):

Minor update to recommended .dockerignore file.

Additional Notes

By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.