refactor: modularize application domains

src/server/app.test.ts

@@ -0,0 +1,12 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createApp } from './app.js';
+
+test('creates isolated Hono applications without starting the server process', () => {
+  const first = createApp();
+  const second = createApp();
+
+  assert.notEqual(first, second);
+  assert.equal(typeof first.fetch, 'function');
+  assert.equal(typeof second.fetch, 'function');
+});