- Add 41 comprehensive test cases covering all functionality
- Test AbschnittTyp model creation and validation
- Test Textabschnitt abstract model through VorgabeLangtext
- Test all rendering types: text, lists, tables, code, diagrams
- Test markdown rendering with footnotes and formatting
- Test table conversion from markdown to Bootstrap HTML
- Test diagram caching with mocked external service calls
- Test diagram error handling and custom options
- Test clear_diagram_cache management command
- Test integration with dokumente models
- All tests passing (41/41)
