When a mixin calls another mixin passing a variable with the same name
as the parameter (e.g., +alert(message) where alert has param message),
skip generating redundant const declaration since the variable is already
in scope.
Also adds missing alert.pug mixin for demo project.
- Add scoped logger (pugz/runtime) for better log filtering
- Add warnings when mixin not found
- Add warnings for mixin attribute failures
- Add warnings for mixin directory/file lookup failures
- Add warnings for mixin parse/tokenize failures
- Use 'action first, then reason' pattern in all log messages
