Breaking change: pip support removed, uv is now required for Python
package management. Install with: curl -LsSf https://astral.sh/uv/install.sh | sh

Fixed:
- Version checking now validates constraints using uv pip install --dry-run
- Previously only checked package existence, not version satisfaction
- Packages needing upgrade are correctly identified and reinstalled
- Bootstrap uses quiet pip install to reduce noise
- Added startup feedback during Python package checks in dev/test

Changed:
- Removed unused config keys (worker timeouts, grpc_test flags)
- Virtual environments created with uv venv for consistency
- Simplified PythonPackages module by removing all pip-specific code paths
- Added SnakeBridge recommendation to README