add package.json for npm git install

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

package.json

@@ -0,0 +1,10 @@
+{
+  "name": "game-sdk",
+  "version": "1.0.0",
+  "description": "Platform SDK for games — window.GameSDK is injected at runtime",
+  "types": "game-sdk.d.ts",
+  "files": [
+    "game-sdk.d.ts",
+    "game-sdk.js"
+  ]
+}