fix: serialize webapp datetime payloads

tests/test_webapp_devices_serialization.py

@@ -0,0 +1,22 @@
+import json
+from datetime import datetime, timezone
+
+import bot.app.web.subscription_webapp  # noqa: F401
+from bot.app.web.webapp.devices import _serialize_device
+
+
+def test_device_serializer_accepts_datetime_created_at():
+    created_at = datetime(2099, 1, 2, 3, 4, tzinfo=timezone.utc)
+
+    payload = _serialize_device(
+        {
+            "hwid": "abcdef123456",
+            "deviceModel": "Laptop",
+            "createdAt": created_at,
+        },
+        1,
+    )
+
+    assert payload["created_at"] == created_at.isoformat()
+    assert payload["created_at_text"] == "02.01.2099 03:04"
+    json.dumps(payload)