Implements several improvements to the qsgen3 site generator:
- **Filename Sanitization**: Introduces robust sanitization for output HTML filenames, converting to lowercase, replacing special characters with hyphens, and ensuring clean names.
- **Blog Post URL Structure**: Blog posts from content/posts/ are now generated with a blog/YYYY/MM/DD/ URL structure if a valid date is present in frontmatter. Defaults to blog/filename.html if no valid date.
- **Improved Title Fallback**: Uses the original filename (before sanitization) as a fallback title if not specified in frontmatter.
- **Enhanced Pandoc Error Handling**: Better logging for Pandoc execution and explicit check of its exit code, allowing the script to continue on single file errors.
- **Sitemap Integration**: Adds successfully generated pages to sitemap URL list.
- **Non-fatal Sitemap Generation**: Sitemap generation failures are now logged as warnings and do not halt the script.
Also, unignores the /scripts/ directory in .gitignore to include migration scripts in the repository.
