Summary

Implement an append method to concatenate or add content to the end of a string.
Should be available via SM facade as both static and fluent usage.

Tasks

• Create AppendTransformer.php in src/Transformers/
• Implement StringTransformerInterface as per project conventions
• Add PHPDoc @method to src/StringMorpher.php
• Add PHPDoc @method to src/Instances/StringMorpherInstance.php
• Add test cases covering core and edge cases in tests/Transformers/
• Add documentation in docs/docs/methods/
• Example usage:

SM::append('foo', 'bar'); // 'foobar'
SM::make('foo')->append('bar'); // 'foobar'

Acceptance Criteria

• Method present, available in facade statically and fluently
• Doc and tests included
• PHPDoc in both facades
• Milestone v1.0.8