test(worker): add vitest harness

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/package.json

@@ -6,7 +6,9 @@
   "scripts": {
     "build": "tsc",
     "start": "node dist/index.js",
-    "dev": "tsx watch src/index.ts"
+    "dev": "tsx watch src/index.ts",
+    "test": "vitest run",
+    "test:watch": "vitest"
   },
   "dependencies": {
     "@prisma/adapter-pg": "^7.4.0",
@@ -23,6 +25,7 @@
     "@types/yauzl": "^2.10.3",
     "prisma": "^7.4.0",
     "tsx": "^4.21.0",
-    "typescript": "^5"
+    "typescript": "^5",
+    "vitest": "^3.2.4"
   }
 }