Website Modernization Migration from Jekyll to Hugo

The preCICE website is built on Jekyll with several Ruby gems that have become difficult to maintain (many of which have been abandoned) and cause frequent build failures for contributors. The goal is to move the site to Hugo (a static site generator built on Go), which handles most of what these plugins do out of the box. This means porting layouts from Liquid to Go templates, upgrading from Bootstrap 3.3.7 to Bootstrap 5, and restructuring content to fit Hugo's model. All existing URLs and external documentation integrations will be kept intact during the transition. Deliverables include a fully functional Hugo site, rewritten CI/CD workflows, Algolia search via JSON output, and sub-repo mounts replacing Jekyll submodules. By the end, any contributor should be able to clone the repo and build the site in one command, with no Ruby setup required.