add multiplayer playmode package

Adds com.unity.multiplayer.playmode 2.0.2 (manifest + lock) for local multi-client testing. Serializes the package's generated PlayMode.meta and VirtualProjectsConfig.json.

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

Packages/packages-lock.json

@@ -89,6 +89,15 @@
         "com.unity.modules.uielements": "1.0.0"
       }
     },
+    "com.unity.multiplayer.playmode": {
+      "version": "2.0.2",
+      "depth": 0,
+      "source": "registry",
+      "dependencies": {
+        "com.unity.nuget.newtonsoft-json": "2.0.2"
+      },
+      "url": "https://packages.unity.com"
+    },
     "com.unity.multiplayer.tools": {
       "version": "2.2.9",
       "depth": 0,