fix: update AISearchServiceTests to pass required NpgsqlDataSource mock

EmbeddingService constructor now requires NpgsqlDataSource (no longer
optional). Tests that construct EmbeddingService for AISearchService
scenarios must supply a mock, even though upload functionality is not
exercised.

Author: BenjaminMichaelis

EssentialCSharp.Chat.Tests/AISearchServiceTests.cs

@@ -33,7 +33,8 @@ private static (AISearchService svc, Mock<VectorStoreCollection<string, BookCont
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(new GeneratedEmbeddings<Embedding<float>>([new Embedding<float>(new float[1536])]));
 
-        var embeddingService = new EmbeddingService(vectorStoreMock.Object, embGenMock.Object);
+        var dataSourceMock = new Mock<NpgsqlDataSource>();
+        var embeddingService = new EmbeddingService(vectorStoreMock.Object, embGenMock.Object, dataSourceMock.Object);
         var loggerMock = new Mock<ILogger<AISearchService>>();
 
         return (new AISearchService(vectorStoreMock.Object, embeddingService, loggerMock.Object), collectionMock);