Fix documentation build in GitHub Actions

Fix the docs Makefile install-deps target to use correct relative path
"../[docs]" instead of ".[docs]" when running from docs/ directory.

This resolves the GitHub Actions docs-test job failure:
"ERROR: file:///home/runner/work/clustrix/clustrix/docs does not appear
to be a Python project: neither 'setup.py' nor 'pyproject.toml' found."

Verified locally that documentation builds successfully with this fix.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: jeremymanning

docs/Makefile

@@ -16,7 +16,7 @@ help:
 
 # Install documentation dependencies
 install-deps:
-	pip install -e ".[docs]"
+	pip install -e "../[docs]"
 
 # Build HTML documentation
 html: install-deps