Implement custom messagebox relevant to 8.0 design

這個 Issue 沒有描述。

The issue names no files, tests, or entry points and provides no implementation details. Start by locating the existing messagebox implementation and the referenced 8.0 design specification. Done means a custom messagebox that matches the approved 8.0 design, but the issue does not define the required behavior or acceptance checks.

由索引模型根據 Issue 內容生成。