로그인 STA 스레드화·SSO 로그아웃·UserInfo 역직렬화 수정 및 AuthTest 추가

- LoginWindow: 로그인/로그아웃/쿠키삭제를 전용 STA 스레드(자체 Dispatcher 펌프)에서 실행
  → SignIn/SignInAsync가 MTA/STA 어느 스레드에서 호출돼도 동작 (RunOnDedicatedUiThreadAsync, AuthenticateAsync)
- SsoClient: 로그인/로그아웃 창을 AuthenticateAsync로 호출, 크로스스레드 Owner 제거
- BaronSSO: SignIn/SignOut을 Task.Run(...).GetAwaiter().GetResult()로 정리, SignInAsync 데드락 주석 추가
- UserInfo: private set 프로퍼티에 [JsonInclude] 적용 → FromSsoFile 역직렬화 복원 정상화, LastAuthTime [JsonIgnore]
- AuthTest 샘플 프로젝트 추가

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

BaronSoftware.SSO.sln

@@ -7,6 +7,8 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BaronSoftware.SSO", "BaronS
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "BaronSoftware.SSO.Sample", "BaronSoftware.SSO.Sample\BaronSoftware.SSO.Sample.csproj", "{6F80A264-7099-3F9E-64A3-89E569A3E7A4}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "AuthTest", "AuthTest\AuthTest.csproj", "{CC253CA9-0F0E-43D9-80D5-CEC2A181E889}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -21,6 +23,10 @@ Global
 		{6F80A264-7099-3F9E-64A3-89E569A3E7A4}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{6F80A264-7099-3F9E-64A3-89E569A3E7A4}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{6F80A264-7099-3F9E-64A3-89E569A3E7A4}.Release|Any CPU.Build.0 = Release|Any CPU
+		{CC253CA9-0F0E-43D9-80D5-CEC2A181E889}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{CC253CA9-0F0E-43D9-80D5-CEC2A181E889}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{CC253CA9-0F0E-43D9-80D5-CEC2A181E889}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{CC253CA9-0F0E-43D9-80D5-CEC2A181E889}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE