fix: preserve subscribe season zero targets (#5983)

tests/test_subscribe_endpoint.py

@@ -42,3 +42,34 @@ class SubscribeEndpointTest(TestCase):
         self.assertTrue(response.success)
         self.assertNotIn("completed_episode", async_add.await_args.kwargs)
         self.assertEqual(async_add.await_args.kwargs["username"], "moviepilot-user")
+
+    def test_create_subscribe_preserves_special_season_zero_with_doubanid(self):
+        """
+        新增订阅带豆瓣 ID 且显式指定 S0 时，标题规整不应覆盖调用方传入的季号。
+        """
+        subscribe_in = Subscribe(
+            name="测试剧集",
+            year="2026",
+            type=MediaType.TV.value,
+            doubanid="12345",
+            season=0,
+            total_episode=5,
+            lack_episode=5,
+        )
+
+        with patch(
+            "app.api.endpoints.subscribe.MetaInfo",
+            return_value=SimpleNamespace(name="测试剧集", begin_season=None),
+        ), patch(
+            "app.api.endpoints.subscribe.SubscribeChain.async_add",
+            new=AsyncMock(return_value=(1, "新增订阅成功")),
+        ) as async_add:
+            response = asyncio.run(
+                create_subscribe(
+                    subscribe_in=subscribe_in,
+                    current_user=SimpleNamespace(name="moviepilot-user"),
+                )
+            )
+
+        self.assertTrue(response.success)
+        self.assertEqual(async_add.await_args.kwargs["season"], 0)