Prompt Template Engine

Build a flexible prompt template engine for production use.

## Requirements
{{template_requirements}}

## Variable Types
{{variable_types}}

## Safety Requirements
{{safety_requirements}}

Implement a complete template system:

```python
class PromptTemplateEngine:
    def __init__(self, templates_dir: str):
        pass
    
    def render(self, template_name: str, variables: dict) -> str:
        """
        Features:
        - Variable substitution
        - Conditional sections
        - Loops for lists
        - Includes/inheritance
        - Escaping and sanitization
        """
        pass
    
    def validate(self, template: str, schema: dict) -> ValidationResult:
        """Validate template syntax and variables"""
        pass
```

Include:
- Jinja2-like syntax support
- Version control integration
- Hot reloading
- Template testing utilities