refactor: replace sortByWeight() with gen-toc output in VitePress pipeline

[VelmiraS]

Prerequisites

• feat: sort manifest node tree by frontmatter weight docforge#487
• Add title to gen-toc output docforge#488

Changes

• Add a gen-toc step to the pipeline (after docforge run and before the VitePress build). It should generate hugo/content/toc.yaml.
• Replace sortByWeight() in sidebar.ts with data from toc.yaml.
• Check whether parts of the post-processing (part-index.js) can also read from toc.yaml instead of scanning the file system.