ci: validate macOS managed behavior on Ubuntu and stabilize shutdown

MeetingAssistant.Tests/MacOsMeetingIntegrationTests.cs

@@ -133,14 +133,9 @@ public sealed class MacOsMeetingIntegrationTests
         Assert.Equal("meeting.png.cropped.png", croppedPath);
     }
 
-    [Fact]
+    [MacOsFact]
     public async Task MacOsCapabilityEndpointReportsEnabledRealProviders()
     {
-        if (!OperatingSystem.IsMacOS())
-        {
-            return;
-        }
-
         await using var factory = new WebApplicationFactory<Program>();
         using var client = factory.CreateClient();
 
@@ -163,14 +158,9 @@ public sealed class MacOsMeetingIntegrationTests
         Assert.True(report.WhisperLocalDiarizationEnabled);
     }
 
-    [Fact]
+    [MacOsFact]
     public async Task NativeHelperAdvertisesCalendarPromptAndScreenshotFeatures()
     {
-        if (!OperatingSystem.IsMacOS())
-        {
-            return;
-        }
-
         var runner = new ProcessCommandRunner(
             NullLogger<ProcessCommandRunner>.Instance);
 
@@ -190,14 +180,9 @@ public sealed class MacOsMeetingIntegrationTests
                 .ToArray());
     }
 
-    [Fact]
+    [MacOsFact]
     public async Task NativeHelperCropsPngUsingOcrPixelCoordinates()
     {
-        if (!OperatingSystem.IsMacOS())
-        {
-            return;
-        }
-
         var testRoot = Path.Combine(
             Path.GetTempPath(),
             $"meeting-assistant-native-crop-{Guid.NewGuid():N}");
@@ -268,14 +253,9 @@ public sealed class MacOsMeetingIntegrationTests
         Assert.Equal(TimeSpan.FromHours(23), client.CalendarTo - client.CalendarFrom);
     }
 
-    [Fact]
+    [MacOsFact]
     public async Task CalendarClientFallsBackToCalendarAutomationWhenEventKitIsDenied()
     {
-        if (!OperatingSystem.IsMacOS())
-        {
-            return;
-        }
-
         var runner = new SequenceCommandRunner(
             new CommandResult(
                 MacOsIntegrationException.CalendarPermissionDeniedExitCode,