doc: add canonical URL pointing to latest/ for SEO

Set html_baseurl so every page emits a rel="canonical" link to the latest/
copy, telling search engines to prefer the latest docs over older versions and
de-duplicating the identical latest/ and 4.0.x/ folders.

Author: the-hampel

doc/conf.py.in

@@ -66,6 +66,12 @@ templates_path = ['@CMAKE_CURRENT_SOURCE_DIR@/_templates']
 html_theme = 'sphinx_rtd_theme'
 html_style = 'css/custom.css'
 
+# Point search engines at the evergreen "latest" build of each page via a
+# rel="canonical" link. Setting this in *every* version build (unstable, X.Y.x,
+# ...) consolidates ranking signals onto the latest/ docs so they are preferred
+# over older versions in search results.
+html_baseurl = 'https://triqs.github.io/solid_dmft/latest/'
+
 html_favicon = '@CMAKE_CURRENT_SOURCE_DIR@/logos/favicon.ico'
 html_logo = '@CMAKE_CURRENT_SOURCE_DIR@/logos/logo_no_text.png'