test(auth): add test-only auth instance with testUtils plugin and initial tests

vitest.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from "vitest/config"
+import path from "path"
+
+export default defineConfig({
+  test: {
+    environment: "node",
+    globals: true,
+    setupFiles: [],
+  },
+  resolve: {
+    alias: {
+      "@": path.resolve(__dirname),
+    },
+  },
+})