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

[jagdep-singh]

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.