test(web): scaffold vitest + RTL with Orchestrator seed suite (DEBT-043)

Wire vitest 4 + jsdom + @testing-library/{react,jest-dom,user-event}
+ @vitest/coverage-v8 through vite.config.ts (defineConfig from
vitest/config). src/test/setup.ts registers jest-dom matchers and
RTL cleanup. tsconfig.app.json picks up vitest/globals types.

Seed suite Orchestrator.test.tsx covers the three regressions
called out in DEBT-043: empty-state render, kind-filter toggling
triggers a scoped refetch, mocked stream callback prepends a row.

decnet_web/src/test/setup.ts

@@ -0,0 +1,7 @@
+import '@testing-library/jest-dom/vitest';
+import { afterEach } from 'vitest';
+import { cleanup } from '@testing-library/react';
+
+afterEach(() => {
+  cleanup();
+});