[Enhancement] 启动器检查更新失败时显示提示

[ToobLac]

• 实例无法验证完整性时不尝试更新且显示提示
• 出现异常时显示检查更新失败提示

[Minecraft269]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces error handling for update checks and disables updates if the launcher instance cannot be verified. Specifically, it adds an error property to UpdateChecker to capture update failures, updates SettingsPage to display these errors or hide the update UI if self-verification fails, and adds corresponding localization strings. The review feedback points out a potential issue in UpdateChecker.java where latestVersion could be incorrectly set to null if finalResult is null, as the original null check was omitted in the new error-handling branch, and suggests restoring this check.

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