test(api): add unit and integration tests for game service and endpoints

- Unit tests for createGameSession and evaluateAnswer (14 tests)
- Endpoint tests for POST /game/start and /game/answer via supertest (8 tests)
- Mock @glossa/db — no real database dependency

apps/api/package.json

@@ -6,7 +6,8 @@
   "scripts": {
     "dev": "tsx watch src/server.ts",
     "build": "tsc",
-    "start": "node dist/server.js"
+    "start": "node dist/server.js",
+    "test": "vitest"
   },
   "dependencies": {
     "@glossa/db": "workspace:*",
@@ -15,6 +16,8 @@
   },
   "devDependencies": {
     "@types/express": "^5.0.6",
+    "@types/supertest": "^7.2.0",
+    "supertest": "^7.2.2",
     "tsx": "^4.21.0"
   }
 }