[FEATURE]: add strong types for py and ts

Add strong types to the A2UI SDK?

I'm currently manipulating dictionaries which is error prone and tedious. At least for things like the A2UI metadata which is fixed per A2UI version.

Look at the A2UI SDK codebase, likely in an 'sdk' or 'client' directory, to understand the current dictionary-based interfaces for metadata. Identify the fixed metadata structure per A2UI version. Create TypeScript type definitions (interfaces/types) and Python type hints (likely using typing module or pydantic) for these structures. Ensure the types are exported/imported correctly. Test by updating a sample usage to use the new types instead of dictionaries.

Written by the indexing model from the issue text.