Refactor ask_user interactions

[F16shen]

Summary

Refactor ask_user to use a structured interaction model and a single shell UI path.

Motivation

ask_user had accumulated legacy compatibility logic and mode-specific UI handling over time. In practice, that caused inconsistent behavior across interaction types, blurred ownership between the tool layer and shell layer, and made it harder to support both strict selection and free-form input cleanly.

This change simplifies the model and makes the interaction flow easier to reason about and extend.

Changes

• introduce structured interaction request/response types
• migrate ask_user onto explicit interaction kinds:
  • single_select
  • text_input
  • choice_or_text
• unify shell-side ask_user handling behind one prompt UI flow
• remove obsolete inline-specific interaction code and stale config
• update tool guidance, docs, and regression coverage

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