Mark live-stream tests as Integration category

CI workflow already filters with --filter "Category!=Integration",
so these tests requiring a local MJPEG stream will be skipped in CI.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: rafalmaciag

src/ModelingEvolution.Mjpeg.Tests/HttpFrameGrabberTests.cs

@@ -3,6 +3,7 @@
 
 namespace ModelingEvolution.Mjpeg.Tests;
 
+[Trait("Category", "Integration")]
 public class HttpFrameGrabberTests
 {
     [Fact]

src/ModelingEvolution.Mjpeg.Tests/MjpegProviderTests.cs

@@ -3,6 +3,7 @@
 
 namespace ModelingEvolution.Mjpeg.Tests;
 
+[Trait("Category", "Integration")]
 public class MjpegProviderTests
 {
     [Fact]