Complete about modal and licensing implementation

- Add comprehensive About & Credits modal with project info and credits
- Download and include Tailwind CSS and Prism.js license files locally
- Add Licenses section to about.html displaying full license texts
- Add license links in credits section pointing to local license files
- Style about button as proper theme-aware button
- Update external resource references to use local files
- Improve offline functionality and license compliance

Author: codebude