Add .gitignore for plugin build artifacts and remove tracked binaries

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,4 +1,17 @@
+# Visual Studio
 Unreal/.vs/
+
+# UE build artifacts (project)
 Unreal/Binaries/
 Unreal/Intermediate/
 Unreal/Saved/
+Unreal/DerivedDataCache/
+
+# UE build artifacts (plugins)
+Unreal/Plugins/*/Binaries/
+Unreal/Plugins/*/Intermediate/
+
+# OS
+Thumbs.db
+Desktop.ini
+.DS_Store