[ReneSchwarzer]

This pull request introduces several documentation improvements, test fixture enhancements, and minor code corrections to the WebExpress project. The most significant updates include expanded documentation on health checks, graceful shutdown, and server entry points, as well as the addition of new health check test fixtures. There are also corrections to the mock identity group policy handling and minor typo and link fixes.

Documentation improvements:

• Expanded the docs/user-guide.md with detailed sections on health checks (including endpoint, component model, and probe configuration), graceful shutdown, public server URI configuration, and server entry point behavior. This provides clearer operational guidance for users and developers.
• Updated documentation links to point to the correct docs/ directory and fixed minor typos (e.g., "Raspberry PI" to "Raspberry Pi", ".net" to ".NET"). Added an AI transparency notice to the README.md. [1] [2] [3] [4]

Health check and test fixture enhancements:

• Added new test health components in TestHealth.cs, including sealed and generic health components to test discovery, dependency injection, and attribute-driven cancellation. This ensures the health check infrastructure is robust and testable.
• Updated the documentation and table of contents to include direct links to the health model section.

Mock identity and policy handling corrections:

• Refactored MockIdentityGroup in test code to use IIdentityPolicy objects instead of string role names for policy assignment and enumeration, aligning with intended usage. [1] [2] [3] [4]
• Fixed a method name in MockIdentityProvider from CreateForbiddenPage to CreateForbiddenResponse for accuracy and clarity.