Add configurable documentation URLs that change based on whether this is
an official release or development build:
- Nix builds:
- Development (officialRelease = false): Use /latest/ URLs
- Official releases (officialRelease = true): Use versioned URLs with
MAJOR.MINOR only (e.g., /2.33/ instead of /2.33.0/)
- Plain meson builds: Default to versioned URLs (official-release = true)
Changes:
- Add --doc-url parameter to expand-includes.py
- Add meson option 'official-release' (defaults to true for Meson builds)
- Compute doc_url in meson.build based on version and official-release
- Forward Nix officialRelease variable to Meson in package.nix
- Update render-manpage.sh to pass doc-url parameter
This allows distros (Fedora, etc.) to have stable versioned URLs by default,
while Nix development builds point to /latest/ for up-to-date documentation.
