fix(app): prevent question dock from auto-scrolling to focused option

When the question dock opens, focus(0) targets the first option button
which sits below the markdown content. The browser auto-scrolls the
overflow container to make the focused element visible, hiding the plan
text. Use preventScroll: true so focus is set for keyboard navigation
without scrolling away from the top.

Author: BYK

packages/app/src/pages/session/composer/session-question-dock.tsx

@@ -160,7 +160,7 @@ export const SessionQuestionDock: Component<{ request: QuestionRequest; onSubmit
     focusFrame = requestAnimationFrame(() => {
       focusFrame = undefined
       const el = next === options().length ? customRef : optsRef[next]
-      el?.focus()
+      el?.focus({ preventScroll: true })
     })
   }