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/vitest.config.ts

@@ -0,0 +1,18 @@
+import { defineConfig } from 'vitest/config'
+import vue from '@vitejs/plugin-vue'
+import { resolve } from 'path'
+
+export default defineConfig({
+  plugins: [vue()],
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, 'src'),
+    },
+  },
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    include: ['src/**/*.test.ts'],
+    setupFiles: ['src/test-setup.ts'],
+  },
+})