Add AVA2-style display options (effect level, trees, clouds)

Client-only port of ENABLE_GRAPHIC_ON_OFF / HIDE_OBJECTS: five effect
levels toggle attached actor effects via Active/Deactive, tree and cloud
parts use background.SetVisiblePart, plus shortcuts for the original
name and damage options. mt_display window, mt_display.cfg, port.display
test, docs/AVA2-DISPLAY.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/port/UserInterface/PythonSystemModule.cpp

@@ -211,6 +211,22 @@ PyObject * systemSetShowSalesTextFlag(PyObject * poSelf, PyObject * poArgs)
 	return Py_BuildNone();
 }
 
+PyObject * systemSetEffectLevel(PyObject * poSelf, PyObject * poArgs)
+{
+	int iLevel;
+	if (!PyTuple_GetInteger(poArgs, 0, &iLevel))
+		return Py_BuildException();
+
+	CPythonSystem::Instance().SetEffectLevel(iLevel);
+
+	return Py_BuildNone();
+}
+
+PyObject * systemGetEffectLevel(PyObject * poSelf, PyObject * poArgs)
+{
+	return Py_BuildValue("i", CPythonSystem::Instance().GetEffectLevel());
+}
+
 PyObject * systemIsAlwaysShowName(PyObject * poSelf, PyObject * poArgs)
 {
 	return Py_BuildValue("i", CPythonSystem::Instance().IsAlwaysShowName());
@@ -422,6 +438,8 @@ void initsystem()
 
 		{ "SetShowSalesTextFlag",		systemSetShowSalesTextFlag,		METH_VARARGS },
 		{ "IsShowSalesText",			systemIsShowSalesText,			METH_VARARGS },
+		{ "SetEffectLevel",				systemSetEffectLevel,			METH_VARARGS }, // PORT: AVA2
+		{ "GetEffectLevel",				systemGetEffectLevel,			METH_VARARGS },
 
 		{ "GetShadowLevel",				systemGetShadowLevel,			METH_VARARGS },
 		{ "SetShadowLevel",				systemSetShadowLevel,			METH_VARARGS },