feat(testing): test harness for @vue-tui/runtime

Provides render() for integration testing — async with auto-flush,
trimmed frames, fake terminal with resize(), stdin.write() with
auto-flush, and auto-cleanup via afterEach.

Exports: render, cleanup, RenderResult, RenderOptions, Terminal

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/testing/tsconfig.json

@@ -0,0 +1,22 @@
+{
+  "compilerOptions": {
+    "target": "esnext",
+    "lib": ["es2023"],
+    "moduleDetection": "force",
+    "module": "nodenext",
+    "moduleResolution": "nodenext",
+    "resolveJsonModule": true,
+    "types": ["node"],
+    "strict": true,
+    "noUnusedLocals": true,
+    "declaration": true,
+    "noEmit": true,
+    "allowImportingTsExtensions": true,
+    "esModuleInterop": true,
+    "isolatedModules": true,
+    "verbatimModuleSyntax": true,
+    "skipLibCheck": true,
+    "jsx": "preserve",
+    "jsxImportSource": "vue"
+  }
+}