Add COOP/COEP support and fix threaded loader script

[kalwalt]

This pull request introduces several improvements to the project, primarily focusing on modernizing the example HTML files, adding local development instructions, and including IDE configuration files. The most significant changes are the refactoring of the ARToolkitNFT_ES6_example.html and ARToolkitNFT_ES6_threading_example.html files to use ES6 modules and import maps, improved handling of cross-origin isolation for threaded examples, and the addition of documentation for local development.

Example HTML modernization and module support:

• Refactored examples/ARToolkitNFT_ES6_example.html and examples/ARToolkitNFT_ES6_threading_example.html to use ES6 modules, import maps for three.js, and module-based script loading, replacing legacy script includes and improving code structure. [1] [2] [3] [4] [5] [6]
• Improved code readability and HTML semantics in both example files (e.g., consistent indentation, lang="en", and video tag formatting). [1] [2]

Cross-origin isolation handling for threading:

• Added a runtime check and reload logic in ARToolkitNFT_ES6_threading_example.html to ensure cross-origin isolation (COOP/COEP) is enabled, which is required for threading support in web workers. This includes user feedback and error handling if isolation cannot be established.

Documentation improvements:

• Updated Readme.md with instructions for local development, including how to serve the site with the necessary COOP/COEP headers for threaded examples, and notes on Netlify configuration.

IDE/editor support:

• Added .idea directory files (.gitignore, modules.xml, vcs.xml, webarkit.github.io.iml) to support JetBrains IDE project configuration and version control integration. [1] [2] [3] [4]

These changes collectively improve the developer experience, modernize the codebase for current JavaScript standards, and ensure compatibility with features that require enhanced browser security settings.