Add required sphinx.configuration to readthedocs.yml

ReadTheDocs now requires explicit sphinx.configuration key.
Set it to docs/conf.py as per the deprecation notice.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: orionarcher

readthedocs.yml

@@ -9,3 +9,6 @@ build:
 
 conda:
   environment: docs/requirements.yaml
+
+sphinx:
+  configuration: docs/conf.py