feat: Step1~Step14 面板单步按钮 EventBus 解耦 + Handler 补全（Step8~Step14）+ 旧上帝类删除

- 9 个面板（step1~step6/step8_ml_train/step8_qaa/step9_ml_predict/step10）单步执行按钮从 parent 链上溯改为 global_event_bus.publish('RequestRunSingleStep')

- PipelineExecutor 新增 _on_request_run_single_step 订阅

- 新增 Handler: step8_ml_train / step9_ml_predict / step10_qaa_inversion / step11_concentration / step12_kriging / step13_visualization / step14_report

- 删除旧 water_quality_inversion_pipeline_GUI.py（上帝类已肢解完毕）

src/gui/water_quality_gui.py

@@ -1244,7 +1244,7 @@ class WaterQualityGUI(QMainWindow):
         if not PIPELINE_AVAILABLE:
             QMessageBox.critical(
                 self, "错误",
-                "无法导入pipeline模块，请确保water_quality_inversion_pipeline_GUI.py文件存在！"
+                "无法导入 Pipeline 模块，请检查 src/core/handlers/ 目录是否完整！"
             )
             return
 
@@ -1400,7 +1400,7 @@ class WaterQualityGUI(QMainWindow):
         if not PIPELINE_AVAILABLE:
             QMessageBox.critical(
                 self, "错误",
-                "无法导入pipeline模块，请确保water_quality_inversion_pipeline_GUI.py文件存在！"
+                "无法导入 Pipeline 模块，请检查 src/core/handlers/ 目录是否完整！"
             )
             return