fix: downgrade Sphinx version from 9.0.4 to 8.1.3 for compatibility

Author: phillipus85

requirements.txt

@@ -120,7 +120,7 @@ six==1.17.0
 smmap==5.0.2
 snowballstemmer==3.0.1
 soupsieve==2.8
-Sphinx==9.0.4
+Sphinx==8.1.3
 sphinx-autoapi==3.6.1
 sphinx-autobuild==2025.8.25
 sphinx-autodoc-typehints==3.6.0