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>

.github/workflows/ci.yml

@@ -33,3 +33,9 @@ jobs:
 
       - name: Lint
         run: pnpm lint
+
+      - name: Security audit
+        run: pnpm audit --audit-level=high
+
+      - name: Server test coverage
+        run: pnpm test -- --run --project server --coverage --coverage.provider=v8 --coverage.reporter=text --coverage.thresholds.lines=30