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_excel.py

@@ -252,6 +252,55 @@ class ExcelImportTests(TempDirMixin, unittest.TestCase):
 
         self.assert_removed(temp_dir)
 
+    def test_write_back_results_writes_new_fields_and_update_status(self):
+        with self.make_temp_dir() as temp_dir:
+            db_path = os.path.join(temp_dir, "cmshopee.db")
+            excel_path = os.path.join(temp_dir, "input.xlsx")
+            self.save_workbook(
+                excel_path,
+                [
+                    (
+                        "待处理任务",
+                        [
+                            ["账号名", "别名", "商品id"],
+                            ["主店", "alias-a", "51100639510"],
+                            ["副店", "alias-b", "51100639511"],
+                            ["未知", "missing", "51100639512"],
+                        ],
+                    )
+                ],
+            )
+            result = excel.import_tasks([excel_path], path=db_path)
+            tasks = db.list_tasks(batch_id=result["batch_id"], path=db_path)
+            for task in tasks:
+                db.set_collected(task.id, "旧标题", "old.jpg", path=db_path)
+                db.set_generated(
+                    task.id,
+                    "新标题" + task.item_id[-2:],
+                    rf"D:\images\{task.item_id}_new.jpg",
+                    path=db_path,
+                )
+            refreshed = db.list_tasks(batch_id=result["batch_id"], path=db_path)
+            db.set_applied(refreshed[0].id, True, path=db_path)
+            db.set_applied(refreshed[1].id, False, "UPDATE_DISABLED", path=db_path)
+            db.mark_skipped(refreshed[2].id, "别名未匹配账号", path=db_path)
+
+            summary = excel.write_back_results(result["batch_id"], path=db_path)
+
+            self.assertEqual(True, summary["ok"])
+            self.assertEqual(1, summary["files"])
+            self.assertEqual(3, summary["rows"])
+            first = self.row_values_by_header(excel_path, row_number=2)
+            second = self.row_values_by_header(excel_path, row_number=3)
+            third = self.row_values_by_header(excel_path, row_number=4)
+            self.assertEqual("新标题10", first["新标题"])
+            self.assertEqual(r"D:\images\51100639510_new.jpg", first["新封面图片路径"])
+            self.assertEqual("成功", first["更新状态"])
+            self.assertEqual("失败：UPDATE_DISABLED", second["更新状态"])
+            self.assertEqual("略过：别名未匹配账号", third["更新状态"])
+
+        self.assert_removed(temp_dir)
+
     def test_export_copy_writes_copy_without_touching_original(self):
         with self.make_temp_dir() as temp_dir:
             db_path = os.path.join(temp_dir, "cmshopee.db")