Add missing type hints to public API classes in card_framework/v2

I noticed that several public-facing classes in `card_framework/v2` don’t currently have full type annotations on their methods.
Adding type hints would improve IDE autocomplete, static analysis, and overall developer experience, without changing any runtime behavior.

Suggested scope:

- `card_framework/v2/card.py`
- `card_framework/v2/header.py`
- `card_framework/v2/section.py`
- Common widgets like `text_paragraph.py`, `image.py`, etc.

This should be a purely additive change (type hints + imports from `typing`) and should not affect existing tests or serialization logic.

If this sounds reasonable, I’d be happy to take this up as a first contribution.

Start by reviewing the public classes in card_framework/v2/card.py, header.py, section.py, and common widgets such as text_paragraph.py and image.py. Identify methods lacking annotations and check nearby typing imports and existing tests before making additive changes. Done means the scoped public API methods have type hints without changing serialization behavior, and the existing tests still pass.

Escrita pelo modelo de indexação a partir do texto da issue.