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/vite.config.ts

@@ -1,9 +1,21 @@
-import { defineConfig } from 'vite'
+import { defineConfig } from 'vitest/config'
 import react from '@vitejs/plugin-react'
 
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [react()],
+  test: {
+    environment: 'jsdom',
+    globals: true,
+    setupFiles: ['./src/test/setup.ts'],
+    css: false,
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'html'],
+      include: ['src/**/*.{ts,tsx}'],
+      exclude: ['src/**/*.d.ts', 'src/test/**', 'src/main.tsx'],
+    },
+  },
   server: {
     proxy: {
       '/api': {