Add backend test harness with mock SQLite

GameList.Tests/Support/StubHttpClientFactory.cs

@@ -0,0 +1,18 @@
+using System.Net.Http;
+
+namespace GameList.Tests.Support;
+
+internal class StubHttpClientFactory : IHttpClientFactory
+{
+    private readonly StubHttpMessageHandler _handler;
+
+    public StubHttpClientFactory(StubHttpMessageHandler handler)
+    {
+        _handler = handler;
+    }
+
+    public HttpClient CreateClient(string name)
+    {
+        return new HttpClient(_handler, dispose: false);
+    }
+}