Rename HITL input metadata field

[abrahmasandra]

Summary

• rename SDK public/core models from ActiveInputRequest/ActiveInputAction to HitlInputMetadata/HitlInputAction
• update response and polling contracts from activeInputRequest to hitlInputMetadata
• preserve callback behavior, dedupe, validation, and test scenarios

Validation

• python -m py_compile on touched SDK files
• ruff check on touched SDK files
• uv run pytest --import-mode=importlib packages/narada/tests/test_agent.py packages/narada/tests/test_cloud_browser.py packages/narada-pyodide/tests/test_cloud_browser.py
• git diff --check
• rg old active input request names: no tracked matches