Prompt Template Library Manager

Build a prompt template library management system.

## Template Categories
{{template_categories}}

## Versioning Requirements
{{versioning_requirements}}

## Access Control
{{access_control}}

Implement the library:

```python
class PromptTemplateLibrary:
    def register_template(self, name: str, template: str, metadata: dict) -> TemplateRef:
        """
        Metadata includes:
        - Category
        - Variables schema
        - Model compatibility
        - Performance benchmarks
        """
        pass
    
    def get_template(self, name: str, version: Optional[str] = None) -> Template:
        """Retrieve specific or latest version"""
        pass
    
    def render(self, name: str, variables: dict) -> str:
        """Render template with variables"""
        pass
    
    def compare_versions(self, name: str, v1: str, v2: str) -> TemplateDiff:
        """Show differences between versions"""
        pass
```

Include:
- Template inheritance
- Variable validation
- Usage analytics
- Deprecation handling