fix: Show actual exceptions in UnoPlatformHost.Run() instead of swallowing them

Co-authored-by: MartinZikmund <1075116+MartinZikmund@users.noreply.github.com>

Author: Copilot

src/Uno.UI.Tests/Hosting/Given_UnoPlatformHost.cs

@@ -0,0 +1,126 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Threading.Tasks;
+using Uno.UI.Hosting;
+
+namespace Uno.UI.Tests.Hosting
+{
+	[TestClass]
+	public class Given_UnoPlatformHost
+	{
+		[TestMethod]
+		public void When_Exception_In_Initialize_Should_Throw_Actual_Exception()
+		{
+			// Arrange
+			var host = new TestHost_ThrowsInInitialize();
+
+			// Act & Assert
+			var exception = Assert.ThrowsException<InvalidOperationException>(() => host.Run());
+			Assert.AreEqual("Test exception in Initialize", exception.Message);
+		}
+
+		[TestMethod]
+		public void When_Exception_In_InitializeAsync_Should_Throw_Actual_Exception()
+		{
+			// Arrange
+			var host = new TestHost_ThrowsInInitializeAsync();
+
+			// Act & Assert
+			var exception = Assert.ThrowsException<InvalidOperationException>(() => host.Run());
+			Assert.AreEqual("Test exception in InitializeAsync", exception.Message);
+		}
+
+		[TestMethod]
+		public void When_Run_With_Async_RunLoop_Should_Throw_InvalidOperationException()
+		{
+			// Arrange
+			var host = new TestHost_AsyncRunLoop();
+
+			// Act & Assert
+			var exception = Assert.ThrowsException<InvalidOperationException>(() => host.Run());
+			Assert.IsTrue(exception.Message.Contains("requires calling 'await host.RunAsync()' instead of 'host.Run()'"));
+		}
+
+		[TestMethod]
+		public void When_Run_With_Synchronous_Completion_Should_Not_Throw()
+		{
+			// Arrange
+			var host = new TestHost_SynchronousCompletion();
+
+			// Act & Assert - should not throw
+			host.Run();
+			Assert.IsTrue(host.InitializeCalled);
+		}
+
+		[TestMethod]
+		public async Task When_RunAsync_With_Exception_Should_Throw_Actual_Exception()
+		{
+			// Arrange
+			var host = new TestHost_ThrowsInInitialize();
+
+			// Act & Assert
+			var exception = await Assert.ThrowsExceptionAsync<InvalidOperationException>(() => host.RunAsync());
+			Assert.AreEqual("Test exception in Initialize", exception.Message);
+		}
+
+		// Test host implementations
+		private class TestHost_ThrowsInInitialize : UnoPlatformHost
+		{
+			protected override void Initialize()
+			{
+				throw new InvalidOperationException("Test exception in Initialize");
+			}
+
+			protected override Task RunLoop()
+			{
+				return Task.CompletedTask;
+			}
+		}
+
+		private class TestHost_ThrowsInInitializeAsync : UnoPlatformHost
+		{
+			protected override void Initialize()
+			{
+				// No-op
+			}
+
+			protected override Task InitializeAsync()
+			{
+				throw new InvalidOperationException("Test exception in InitializeAsync");
+			}
+
+			protected override Task RunLoop()
+			{
+				return Task.CompletedTask;
+			}
+		}
+
+		private class TestHost_AsyncRunLoop : UnoPlatformHost
+		{
+			protected override void Initialize()
+			{
+				// No-op
+			}
+
+			protected override async Task RunLoop()
+			{
+				await Task.Delay(100); // Simulate async operation
+			}
+		}
+
+		private class TestHost_SynchronousCompletion : UnoPlatformHost
+		{
+			public bool InitializeCalled { get; private set; }
+
+			protected override void Initialize()
+			{
+				InitializeCalled = true;
+			}
+
+			protected override Task RunLoop()
+			{
+				return Task.CompletedTask;
+			}
+		}
+	}
+}