feat: 完成T-303 AI批量生成

- 新增 generate_batch，先并发生成标题再并发生成封面，成功逐条 set_generated 落库

- Tab② 接入开始生成、停止、进度展示和双击新旧封面预览

- 新增 GenerateWorker，通过 worker signal 回传进度与行刷新

- 补充批量生成成功、失败、停止取消和 GUI worker 单元测试

- 同步任务看板、API、路由、当前状态与 progress 文档

tests/test_gui.py

@@ -22,6 +22,7 @@ from app.gui import (
     AccountsTab,
     CollectWorker,
     CollectTab,
+    GenerateWorker,
     GenerateTab,
     MainWindow,
     TAB_STYLE,
@@ -91,6 +92,10 @@ class GuiTests(TempDirMixin, unittest.TestCase):
             self.assertEqual("标题提示词", tab.title_prompt_edit.placeholderText())
             self.assertEqual("封面提示词", tab.cover_prompt_edit.placeholderText())
             self.assertEqual("保存标题提示词", tab.save_title_button.text())
+            self.assertEqual("开始生成", tab.generate_button.text())
+            self.assertEqual("停止", tab.stop_generate_button.text())
+            self.assertFalse(tab.stop_generate_button.isEnabled())
+            self.assertEqual("进度：标题0/0 · 封面0/0 · 失败0", tab.progress_label.text())
             self.assertEqual("默认", tab.cover_template_combo.currentText())
             self.assertEqual(["店铺", "商品ID", "旧标题", "新标题", "状态"], tab.model.HEADERS)
             self.assertEqual("任务 0/0 条", tab.summary_label.text())
@@ -161,6 +166,10 @@ class GuiTests(TempDirMixin, unittest.TestCase):
                 tab.preview_cover_prompt()
             self.assertIn("预览 旧标题 新标题 51100639510 主店", info.call_args[0][2])
 
+            with mock.patch("app.gui.QDialog.exec", return_value=0) as exec_dialog:
+                tab.show_task_images(tab.model.index(0, 0))
+            exec_dialog.assert_called_once()
+
             tab.cover_prompt_edit.moveCursor(QTextCursor.End)
             tab.insert_title_placeholder()
             self.assertTrue(tab.cover_prompt_edit.toPlainText().endswith("{新标题}"))
@@ -171,6 +180,59 @@ class GuiTests(TempDirMixin, unittest.TestCase):
 
         self.assert_removed(temp_dir)
 
+    def test_generate_worker_calls_generate_batch_and_emits_signals(self):
+        with self.make_temp_dir() as temp_dir:
+            cfg = self.make_config(temp_dir)
+            account = accounts.create_account("主店", "alias-a", debug_port=9222, config=cfg)
+            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"])
+            tasks = db.list_tasks(batch_id=batch_id, path=cfg["db_path"])
+            progress = []
+            rows = []
+
+            def fake_generate_batch(tasks_arg, prompt_values, ai_cfg=None, on_progress=None, should_stop=None):
+                self.assertEqual(tasks, tasks_arg)
+                self.assertEqual({"title": "标题提示", "cover": "封面提示"}, prompt_values)
+                self.assertEqual(account, ai_cfg["account_by_alias"]["alias-a"])
+                self.assertEqual(cfg["db_path"], ai_cfg["db_path"])
+                self.assertFalse(should_stop())
+                on_progress({"total": 1, "title_done": 1, "cover_done": 0, "failed": 0})
+                ai_cfg["on_task_update"](tasks[0].id, {"stage": "generated"})
+                return {"ok": True, "total": 1, "title_done": 1, "cover_done": 1, "failed": 0}
+
+            worker = GenerateWorker(
+                tasks,
+                {"title": "标题提示", "cover": "封面提示"},
+                db_path=cfg["db_path"],
+                config=cfg,
+            )
+            worker.progress.connect(progress.append)
+            worker.row_updated.connect(lambda task_id, fields: rows.append((task_id, fields)))
+
+            with mock.patch("app.gui.ai.generate_batch", side_effect=fake_generate_batch):
+                summary = worker.execute()
+
+            self.assertEqual(1, summary["cover_done"])
+            self.assertEqual([{"total": 1, "title_done": 1, "cover_done": 0, "failed": 0}], progress)
+            self.assertEqual([(tasks[0].id, {"stage": "generated"})], rows)
+
+        self.assert_removed(temp_dir)
+
     def test_generate_tab_lists_tasks_and_filters_by_shop_status_and_batch(self):
         with self.make_temp_dir() as temp_dir:
             cfg = self.make_config(temp_dir)