## Summary
Several docs pages rendered identical `<title>` tags, which weakens
search indexing and makes results ambiguous. Each affected page now has
a unique, descriptive title while keeping its existing sidebar label
unchanged.
Alongside the retitles:
- Removed two stale build-system upgrade pages that were no longer in
the navigation, with redirects to the current package upgrade guide.
- Redirected the build-extensions group index to its overview page so
the two URLs stop sharing a title.
- Dropped a leftover orphaned API reference page (its old URL already
redirects to the management overview).
No links break: nothing in the docs points at the removed pages, and
every redirect target exists.
DKP
8d321f8d6e