(bugfix) Preserve existing schedule values in the edit form

Only apply default schedule initial values when creating a new schedule.

Avoid passing default initial data while editing an existing ScheduleConfig,
so the form renders the active cron-style expression, user, and retention
settings from the database.

Add a regression test that reopens an existing schedule and verifies the
stored values are shown instead of defaults.

src/pobsync_backend/tests/test_views.py

@@ -1203,6 +1203,26 @@ class ViewTests(TestCase):
         self.assertFalse(schedule.prune)
         self.assertEqual(schedule.prune_max_delete, 8)
 
+    def test_schedule_form_renders_existing_schedule_values(self) -> None:
+        self.client.force_login(self.staff_user)
+        host = HostConfig.objects.create(host="web-01", address="web-01.example.test")
+        ScheduleConfig.objects.create(
+            host=host,
+            cron_expr="45 4 * * 1",
+            user="backup",
+            enabled=True,
+            prune_max_delete=8,
+        )
+
+        response = self.client.get(reverse("edit_host_schedule", args=[host.host]))
+
+        self.assertEqual(response.status_code, 200)
+        self.assertContains(response, "Edit Schedule")
+        self.assertContains(response, 'value="45 4 * * 1"', html=False)
+        self.assertContains(response, 'value="backup"', html=False)
+        self.assertContains(response, 'value="8"', html=False)
+        self.assertNotContains(response, 'value="15 2 * * *"', html=False)
+
     def test_schedule_form_rejects_invalid_cron(self) -> None:
         self.client.force_login(self.staff_user)
         host = HostConfig.objects.create(host="web-01", address="web-01.example.test")