test: add test infrastructure for frontend and server

- Frontend: vitest.config.ts with vue plugin + jsdom, dummy component test
- Server: in-memory SQLite test DB factory + Hono testClient helper + smoke test
- CI: add pnpm audit and server coverage threshold steps
- Root: vitest workspace config for multi-project test discovery

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

frontend/package.json

@@ -16,7 +16,10 @@
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.2.1",
+    "@testing-library/vue": "^8.1.0",
     "@vitejs/plugin-vue": "^5.2.3",
+    "@vue/test-utils": "^2.4.6",
+    "jsdom": "^28.1.0",
     "tailwindcss": "^4.2.1",
     "typescript": "^5.7.3",
     "vite": "^7.3.1",