This pull request improves documentation and testing for the vscode-ddev-phpstan project. The most significant changes include the addition of detailed Copilot instructions for contributors, updates to the user documentation to clarify configuration behavior, and enhancements to TypeScript test code for better error typing and assertion clarity.

Documentation improvements:

• Added a comprehensive .github/copilot-instructions.md file to guide Copilot and contributors on project architecture, coding guidelines, and common tasks.
• Updated README.md to clarify how the extension handles the configPath setting, including auto-detection of configuration files and the precedence of settings. [1] [2]
• Increased the minimum VS Code version requirement in README.md from 1.100.0 to 1.108.0.

Testing and code quality:

• Improved TypeScript test code in src/test/ddev-utils.test.ts by introducing a dedicated ExecDdevError interface for error handling and using stricter assertion methods for better type safety and clarity. [1] [2] [3]