Add Main Menu UI, alien models & editor configs

Add VS Code workspace/launch/settings for Unity development and a new MainMenu scene/UI (uxml, uss, tss) with MainMenuController and related assets. Import two alien character FBX models (with generated .meta settings) and add folder metadata. Update Git LFS pointers for a Game Kit scene and add modifications to Game Kit Controller assets (World Canvas material and Save Camera render texture) and ProjectSettings/QualitySettings. These changes bring initial UI/menu assets and character models into the project and add editor tooling/config for easier development.

.vscode/extensions.json

@@ -0,0 +1,5 @@
+{
+    "recommendations": [
+      "visualstudiotoolsforunity.vstuc"
+    ]
+}