fix: 配置模块可靠性加固

[JusterZhu]

Summary

Closes#87

对配置管理模块进行完整审查并修复 6 个可靠性风险。

修复详情

#	风险	严重度	修复
1	手动编辑 config.json 输入非法 AuthScheme 枚举值	HIGH	AppConfig.Sanitize() + AuthCredential.Sanitize() 自动校验修复
2	Load() 仅 catch JsonException，磁盘满/权限拒绝导致启动崩溃	HIGH	扩展为 catch IOException + UnauthorizedAccessException
3	12 处 fire-and-forget SaveAsync 调用，I/O 失败静默丢失	HIGH	SafeFireAndForgetSave() 包裹 Task.Run + try-catch + Trace 日志
4	窗口关闭用 Task.Run 异步写盘，进程退出前可能未完成	HIGH	改为同步 Save()，<1ms 完成
5	PatchViewModel 构造函数触发不必要的 SaveAsync	MEDIUM	添加 _initialized 守卫
6	LoadAsync() 两条路径漏调 Sanitize()	MEDIUM	补全调用

文件变更

• 12 files changed, +108 -37
• dotnet build: 0 errors

关键新增

// 配置加载后自动修复（AppConfig.cs）internalvoidSanitize(){UploadAuth??=newAuthCredential();SimulationAuth??=newAuthCredential();if(UploadTimeoutSeconds<10)UploadTimeoutSeconds=300;if(UploadRetryCountis<0 or >10)UploadRetryCount=3;UploadAuth.Sanitize();SimulationAuth.Sanitize();}// 安全的 fire-and-forget 保存（ConfigService.cs）publicstaticvoidSafeFireAndForgetSave(ConfigServiceservice){_=Task.Run(async()=>{try{awaitservice.SaveAsync();}catch(Exceptionex){Trace.WriteLine($"Config save failed: {ex.Message}");}});}

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