build: vitest config (node env, src/**/*.test.ts)

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

vitest.config.ts

@@ -0,0 +1,11 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+    test: {
+        environment: 'node',
+        include: ['src/**/*.test.ts'],
+        globals: false,
+        reporters: ['default'],
+        clearMocks: true,
+    }
+});