agent_ui: Disable pickers while thread is generating (#50519)

It does not make sense to enable them during the running turn and it can
lead to more confusing states if subagents are used.

Release Notes:

- N/A

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Co-authored-by: Danilo Leal <daniloleal09@gmail.com>
dd0e51ecb8Bennet Bo Fenner committed on 3/12/2026, 10:24:38 PM· committed by GitHubparentb32067d
3 files changedLine totals unavailable