Phase 4: Add pre-commit hook to prevent new markdown files in docs/source/

Co-authored-by: leofang <5534781+leofang@users.noreply.github.com>

Author: Copilot

.pre-commit-config.yaml

@@ -30,6 +30,14 @@ repos:
         language: python
         additional_dependencies:
           - https://files.pythonhosted.org/packages/cc/20/ff623b09d963f88bfde16306a54e12ee5ea43e9b597108672ff3a408aad6/pathspec-0.12.1-py3-none-any.whl
+      
+      - id: no-markdown-in-docs-source
+        name: Prevent markdown files in docs/source directories
+        entry: bash -c
+        args: ['if find . -path "*/docs/source/*.md" -not -path "./docs/README.md" | grep -q .; then echo "ERROR: Markdown files found in docs/source/ directories. Use reStructuredText (.rst) instead."; exit 1; fi']
+        language: system
+        pass_filenames: false
+        always_run: true
 
   - repo: https://github.com/PyCQA/bandit
     rev: 2d0b675b04c80ae42277e10500db06a0a37bae17  # frozen: 1.8.6