[sbglasius]

This pull request upgrades the project to Grails 8 and Java 21, modernizes dependencies, updates the Gradle wrapper, and improves test coverage for relative asset URLs in rendering. It also simplifies logging configuration and updates asset versions for better compatibility.

Framework and Build System Upgrades:

• Upgraded the project and example app from Grails 7 to Grails 8, and from Java 17 to Java 21, including updating the relevant properties in gradle.properties, example/gradle.properties, and workflow files (.github/workflows/gradle.yml, .github/workflows/release.yml). [1] [2] [3] [4] [5]
• Updated the Gradle wrapper to version 9.8.0 in both the main and example projects, including associated script changes for gradlew and gradlew.bat. [1] [2] [3]

Dependency and Asset Updates:

• Upgraded JavaScript and CSS dependencies: updated jQuery to 4.0.0 and Bootstrap to 5.3.8 in the example app's assets. [1] [2]
• Updated build configuration in example/build.gradle for Java version handling and added missing test fixture dependency. [1] [2]

Logging and Configuration:

• Removed the logback-spring.xml file and replaced logging configuration with a simplified YAML-based approach in application.yml. [1] [2]

Testing and Rendering Improvements:

• Added new integration and PDF rendering tests to verify that relative URLs in inline styles resolve correctly against the base URL, including a new template and test methods. [1] [2] [3] [4]

Minor Fixes and Cleanups:

• Updated navigation link in the main layout to use Grails' createLink for better routing.
• Minor copyright and script documentation updates in wrapper scripts.

These changes collectively modernize the codebase, ensure compatibility with the latest Grails and Java versions, and improve the reliability of asset rendering and testing.