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/src/test-setup.ts

@@ -0,0 +1,2 @@
+// Frontend test setup for @vue/test-utils + jsdom
+// Add global test utilities and mocks here as needed