AskUserQuestion preview panels should be scrollable when content is truncated

Problem

When AskUserQuestion uses the markdown preview option (side-by-side layout with options on the left and a code preview on the right), the preview panel truncates long content and shows "N lines hidden". There is no way to scroll the preview pane — arrow keys only switch between options on the left side.

This means users are asked to choose between options based on code previews they literally cannot read fully. This defeats the purpose of having previews.

Expected behavior

The preview panel should be scrollable (e.g., with arrow keys, j/k, or page up/down while the preview is focused) so users can read the full content before making a selection.

Steps to reproduce

1. Have a tool call AskUserQuestion with markdown previews containing ~30+ lines of code
2. Observe the preview panel shows "N lines hidden"
3. Try to scroll — no keybinding works to reveal the hidden content

Environment

• Claude Code CLI
• Any terminal size where preview content exceeds available height

Evidence

  ☐ Input types

  How should we handle the two kinds of input?

  ❯ 1. :schema for caller args,     ┌───────────────────────────────────────────────────┐
      :input for upstream           │ (deftool lint-check                               │
      (Recommended)                 │   "Run linter"                                    │
    2. Only :schema, no :input      │   :schema [:map [:cwd :string]]  ;; caller args   │
    3. :schema for everything       │   :input  [:map [:git-summary :any]]  ;; upstream │
                                    │   :output [:map [:findings [:vector Finding]]]    │
                                    │   :params [{:keys [cwd]} _sys]                    │
                                    ├─── ✂ ─── 10 lines hidden ─────────────────────────┤