feat: 完成T-403结果回写与汇总

新增excel.write_back_results，按原Excel文件、工作表和行号回写新标题、新封面图片路径与更新状态。

③更新完成后自动用WriteBackWorker(mode=results)回写结果，并弹窗汇总成功、失败、略过数量；文件被占用时提示关闭Excel后手动重试。

补充Excel结果回写、GUI自动回写/汇总/锁文件提示和模块契约测试，同步任务看板、API、流程和当前状态文档。

tests/test_gui.py

@@ -515,7 +515,15 @@ class GuiTests(TempDirMixin, unittest.TestCase):
 
             self.assertEqual(["alias-a", "alias-b"], applied_aliases)
             self.assertEqual(
-                {"ok": False, "total": 3, "done": 3, "applied": 1, "skipped": 1, "failed": 1},
+                {
+                    "ok": False,
+                    "total": 3,
+                    "done": 3,
+                    "applied": 1,
+                    "skipped": 1,
+                    "failed": 1,
+                    "batch_ids": [batch_id],
+                },
                 summary,
             )
             self.assertEqual(
@@ -538,6 +546,97 @@ class GuiTests(TempDirMixin, unittest.TestCase):
 
         self.assert_removed(temp_dir)
 
+    def test_apply_tab_auto_starts_result_write_back_and_shows_summary(self):
+        with self.make_temp_dir() as temp_dir:
+            cfg = self.make_config(temp_dir)
+            db.init_db(cfg["db_path"])
+            batch_id = db.create_batch(["input.xlsx"], path=cfg["db_path"])
+            db.insert_tasks(
+                batch_id,
+                [
+                    {
+                        "source_file_abs": os.path.join(temp_dir, "input.xlsx"),
+                        "source_sheet": "商品",
+                        "source_row": 2,
+                        "account_name": "Excel主店",
+                        "alias": "alias-a",
+                        "item_id": "51100639510",
+                    }
+                ],
+                path=cfg["db_path"],
+            )
+            task = db.list_tasks(batch_id=batch_id, path=cfg["db_path"])[0]
+            db.set_collected(task.id, "旧标题", "old.jpg", path=cfg["db_path"])
+            db.set_generated(task.id, "新标题", "new.jpg", path=cfg["db_path"])
+            db.set_applied(task.id, True, path=cfg["db_path"])
+            statuses = []
+            tab = ApplyTab(config=cfg, status_callback=statuses.append)
+            self.addCleanup(tab.close)
+            payload = {
+                "done": 1,
+                "total": 1,
+                "applied": 1,
+                "failed": 0,
+                "skipped": 0,
+                "batch_ids": [batch_id],
+            }
+
+            with mock.patch.object(tab, "_start_result_write_back", return_value=True) as start_write_back:
+                tab._on_apply_finished(payload)
+
+            start_write_back.assert_called_once_with(
+                [batch_id],
+                auto=True,
+                apply_summary=payload,
+            )
+            self.assertIn("正在自动回写结果到 Excel", statuses[-1])
+
+        self.assert_removed(temp_dir)
+
+    def test_apply_tab_result_write_back_finished_shows_completion_popup(self):
+        with self.make_temp_dir() as temp_dir:
+            statuses = []
+            tab = ApplyTab(config=self.make_config(temp_dir), status_callback=statuses.append)
+            self.addCleanup(tab.close)
+            summary = {"applied": 2, "failed": 1, "skipped": 1}
+            write_back_payload = {"ok": True, "files": 1, "rows": 4}
+
+            with mock.patch("app.gui.QMessageBox.information") as info:
+                tab._on_result_write_back_finished(
+                    write_back_payload,
+                    auto=True,
+                    apply_summary=summary,
+                )
+
+            message = info.call_args[0][2]
+            self.assertIn("成功：2，失败：1，略过：1", message)
+            self.assertIn("Excel 回写：文件1，行4", message)
+            self.assertIn("Excel 自动回写更新结果完成", statuses[-1])
+
+        self.assert_removed(temp_dir)
+
+    def test_apply_tab_result_write_back_locked_file_message_points_to_manual_retry(self):
+        with self.make_temp_dir() as temp_dir:
+            statuses = []
+            tab = ApplyTab(config=self.make_config(temp_dir), status_callback=statuses.append)
+            self.addCleanup(tab.close)
+            summary = {"applied": 1, "failed": 0, "skipped": 0}
+
+            with mock.patch("app.gui.QMessageBox.warning") as warning:
+                tab._on_result_write_back_failed(
+                    -1,
+                    "Excel 文件被占用，请关闭后重试: input.xlsx",
+                    auto=True,
+                    apply_summary=summary,
+                )
+
+            message = warning.call_args[0][2]
+            self.assertIn("成功：1，失败：0，略过：0", message)
+            self.assertIn("点击「回写结果到 Excel」手动重试", message)
+            self.assertIn("手动重试", statuses[-1])
+
+        self.assert_removed(temp_dir)
+
     def test_apply_worker_preflight_blocks_when_chrome_not_running(self):
         with self.make_temp_dir() as temp_dir:
             cfg = self.make_config(temp_dir)
@@ -1246,6 +1345,20 @@ class GuiTests(TempDirMixin, unittest.TestCase):
             path="db.sqlite",
         )
 
+    def test_write_back_worker_calls_result_write_back(self):
+        with mock.patch(
+            "app.gui.excel.write_back_results",
+            return_value={"ok": True, "batch_id": "batch-1", "files": 1, "rows": 2},
+        ) as write_back_results:
+            summary = WriteBackWorker("batch-1", db_path="db.sqlite", mode="results").execute()
+
+        self.assertEqual({"ok": True, "batch_id": "batch-1", "files": 1, "rows": 2}, summary)
+        write_back_results.assert_called_once_with(
+            "batch-1",
+            excel_path=None,
+            path="db.sqlite",
+        )
+
 
 if __name__ == "__main__":
     unittest.main()