Why do you allow generating a diagram with any theme, but validate only known themes from the list when saving in .env? What is the logic behind this approach?

Allowing the generation of diagrams with any theme is useful for flexibility and experimentation — users can try different visualization options without restrictions.

However, when saving in .env, it is important to validate themes against a list of known ones to:

• Ensure consistency and predictable application behavior.
• Avoid errors due to typos or unsupported themes when loading configuration.
• Facilitate maintenance and debugging, as the list of themes is fixed and controlled.

Thus, free generation is for convenience and creativity, while strict validation upon saving is for reliability and stable operation.