fix(question): register answer channel before prompt event

[cursor]

Summary

Fixes a race introduced by the oneshot question-response refactor. The evolve loop previously emitted the question event before registering the pending oneshot sender, so a fast UI choice could call darwin_evolve_answer while no pending question existed. That rejected the answer, the UI marked it answered, and the backend could wait indefinitely.

This registers the response receiver before emitting the question event and then awaits that prepared receiver.

Test Plan

• Added prepared_question_response_accepts_immediate_answer regression coverage.
• Attempted cargo +stable test prepared_question_response_accepts_immediate_answer in the Linux cloud environment. It is blocked by existing unrelated Linux build errors in Tauri window code (hidden_title, RunEvent::Reopen, and unused variable: window under unused = deny).
• cargo +stable test --lib ... is not available because the package has no library target.

Docs

• No docs update needed

  

[github-actions]

	Warnings
⚠️	Please assign this PR to someone (usually yourself).

	Messages
📖	No docs update needed — acknowledged.

📋 PR Overview

Lines changed	38 (+35 / -3)
Files	0 added, 2 modified, 0 deleted
Draft / WIP	no
Has Test Plan	yes
New UI components	no
New Storybook stories	no
New Rust modules	no
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

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[Scott McMaster (scottmcmaster)]

This seems valid but the suggested PR fails the build, so I will pull it and fix it up.