Add request-user-input overlay (#9585)

- Add request-user-input overlay and routing in the TUI

docs/tui-request-user-input.md

@@ -0,0 +1,39 @@
+# Request user input overlay (TUI)
+
+This note documents the TUI overlay used to gather answers for
+`RequestUserInputEvent`.
+
+## Overview
+
+The overlay renders one question at a time and collects:
+
+- A single selected option (when options exist).
+- Freeform notes (always available).
+
+When options are present, notes are stored per selected option and the first
+option is selected by default, so every option question has an answer. If a
+question has no options and no notes are provided, the answer is submitted as
+`skipped`.
+
+## Focus and input routing
+
+The overlay tracks a small focus state:
+
+- **Options**: Up/Down move the selection and Space selects.
+- **Notes**: Text input edits notes for the currently selected option.
+
+Typing while focused on options switches into notes automatically to reduce
+friction for freeform input.
+
+## Navigation
+
+- Enter advances to the next question.
+- Enter on the last question submits all answers.
+- PageUp/PageDown navigate across questions (when multiple are present).
+- Esc interrupts the run.
+
+## Layout priorities
+
+The layout prefers to keep the question and all options visible. Notes and
+footer hints collapse as space shrinks, with notes falling back to a single-line
+"Notes: ..." input in tight terminals.