Add local time handling for ETA calculations and tests

backend/test/etaTimezone.test.js

@@ -0,0 +1,16 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const { ETA_TIME_ZONE, getIsoWeekday, getLocalDateTime } = require('../src/utils/etaTime');
+
+test('ETA uses Europe/Minsk local date and time instead of UTC', () => {
+  const utcDate = new Date('2026-07-10T21:30:15.000Z');
+
+  assert.equal(ETA_TIME_ZONE, 'Europe/Minsk');
+  assert.deepEqual(getLocalDateTime(utcDate), {
+    date: '2026-07-11',
+    time: '00:30:15',
+    hour: 0
+  });
+  assert.equal(getIsoWeekday(utcDate), 6);
+});