Add Drupal Expert Agent chat mode.

[spectatora]

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.

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Description

This PR adds a comprehensive Drupal Expert chatmode that provides expert guidance for Drupal development, architecture, and best practices.

What This Chatmode Does

The Drupal Expert chatmode transforms GitHub Copilot into a specialized Drupal development assistant with deep knowledge of:

• Drupal core architecture (plugins, service container, entity API, routing, hooks, events)
• Modern PHP 8.3+ development patterns
• Custom module and theme development
• Security best practices and performance optimization
• Testing strategies with PHPUnit
• Configuration management and deployment workflows

Key Features

• Comprehensive Code Examples: Includes working examples for custom entities, block plugins, services, controllers, event subscribers, and more
• Best Practices: Covers Drupal coding standards, security patterns, caching strategies, and dependency injection
• Practical Commands: Provides Drush commands, testing commands, and deployment guidance
• Advanced Topics: Covers service decoration, queue API, typed data API, and custom plugin types

Usage Notes

This chatmode is ideal for:

• Drupal developers building custom modules and themes
• Teams maintaining Drupal applications
• Developers migrating to modern Drupal patterns
• Anyone needing expert guidance on Drupal architecture and best practices

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Type of Contribution

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

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Additional Notes

File Created: chatmodes/drupal-expert.chatmode.md
README Update: The update-readme.js script has been run successfully, and the new chatmode is now listed in README.chatmodes.md with proper installation badges.

The chatmode provides 688 lines of comprehensive guidance, making it one of the most detailed technical expert chatmodes in the repository, comparable to the PHP MCP Expert chatmode in depth and structure.

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