chore: add CODEOWNERS file for code review automation

Defines @promptfoo/engineering as code owners for:
- All files (global)
- Python source code (/src/)
- CI/CD workflows (/.github/)
- Package configuration (pyproject.toml)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: claude

.github/CODEOWNERS

@@ -0,0 +1,14 @@
+# Code owners for promptfoo-python
+# These owners will be automatically requested for review when someone opens a pull request
+
+# Global owners
+* @promptfoo/engineering
+
+# Python source code
+/src/ @promptfoo/engineering
+
+# CI/CD workflows
+/.github/ @promptfoo/engineering
+
+# Package configuration
+/pyproject.toml @promptfoo/engineering