- Add new template package to handle variable substitution with {{variable}} syntax
- Move substitution logic from patterns to centralized template system
- Update patterns.go to use template package for variable processing
- Support special {{input}} handling for pattern content
- Update chatter.go and rest API to pass input parameter
- Enable multiple passes to handle nested variables
- Report errors for missing required variables
This change sets up a foundation for future templating features like front matter
and plugin support while keeping the substitution logic centralized.
