Fix settings restart prompt lost after language/skin change

[QueryOfficial]

Summary

Persist the settings "restart required" prompt across Interface tab locale/skin rebuilds so changing resolution (or other restart-required options) still prompts after switching language/skin.

Previously ShowRestartQuestion() showed a QuestionBox owned by MainMenu. Changing language or skin destroys and recreates MainMenu, which dropped that prompt. The restart requirement is now tracked on CLocalGUI and re-shown after the UI rebuild.

Motivation

Fixes #5063
When a user changed screen resolution in Video settings, then switched to the Interface tab and changed language (or skin), closing settings no longer asked to restart — even though the resolution change still required one.

Root cause: locale/skin changes call DestroyWindows() / CreateWindows(), which replaces MainMenu and its QuestionBox, so the restart dialog was lost and never restored.

Test plan

1. Open Settings → Video → change resolution only → OK → restart prompt appears.
2. Open Settings → Video → change resolution → Interface → change language → OK → after language reload, RESTART REQUIRED appears in the new language.
3. Repeat step 2 with a skin change instead of language → restart prompt appears after the UI rebuild.
4. Change language only (no restart-required setting) → no restart prompt.
5. On the restart prompt, choose No → client continues; choose Yes → client restarts.
6. Confirm dialog strings match the existing locale translations.

Checklist

• Your code should follow the coding guidelines.
• Smaller pull requests are easier to review. If your pull request is beefy, your pull request should be reviewable commit-by-commit.

[DateFTP]

Thank you for fixing the bugfix, as I started encountering this bug with the latest 1.6 build. It's a good thing I added the issues to the bugfix wait list.

[QueryOfficial]

Thank you for fixing the bugfix, as I started encountering this bug with the latest 1.6 build. It's a good thing I added the issues to the bugfix wait list.

I follow the issues created in my free time and try to address them as much as I can.