fix: PanelFactory 信号风暴修复 + 后端上帝类肢解（BaseStepHandler/调度器/Step1打样）

src/gui/core/panel_factory.py

@@ -162,14 +162,19 @@ class PanelFactory:
         scroll.setWidget(panel)
         scroll.setWidgetResizable(True)
 
-        # 替换占位页
+        # 替换占位页（blockSignals 阻断 removeTab/insertTab/setCurrentIndex 触发的
+        # currentChanged 信号风暴，防止 _on_tab_changed → _ensure_loaded 无限递归）
         placeholder = self._placeholders.get(tab_index)
         if placeholder is not None and self._tab_widget is not None:
             tab_title = self._tab_widget.tabText(tab_index)
             tab_icon = self._tab_widget.tabIcon(tab_index)
-            self._tab_widget.removeTab(tab_index)
-            self._tab_widget.insertTab(tab_index, scroll, tab_icon, tab_title)
-            self._tab_widget.setCurrentIndex(tab_index)
+            self._tab_widget.blockSignals(True)
+            try:
+                self._tab_widget.removeTab(tab_index)
+                self._tab_widget.insertTab(tab_index, scroll, tab_icon, tab_title)
+                self._tab_widget.setCurrentIndex(tab_index)
+            finally:
+                self._tab_widget.blockSignals(False)
 
         # 注册
         self._panels[step_id] = panel