feat: split Install/UnitTest stages, add game.js tests with 100% coverage

21 tests covering win/loss/draw/score/reset. lcov report fed to SonarQube.
Pipeline: Install → Unit Test → Scan Code Quality → Build & Push.

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

package.json

@@ -5,13 +5,19 @@
   "main": "index.js",
   "scripts": {
     "start": "node index.js",
-    "test": "jest"
+    "test": "jest --coverage"
   },
   "dependencies": {
     "express": "^4.18.2"
   },
   "devDependencies": {
     "jest": "^29.5.0",
+    "jest-environment-jsdom": "^29.5.0",
     "supertest": "^6.3.3"
+  },
+  "jest": {
+    "collectCoverageFrom": ["index.js", "public/game.js"],
+    "coverageReporters": ["lcov", "text"],
+    "coverageDirectory": "coverage"
   }
 }