2V0-f: run the real system.py app loop in Godot

- system.py runs app.Loop() on the script fiber; each UIUpdate is one
  CPythonApplication::Process(). Logo -> Login, popup ESC/click and
  app.Exit teardown (launcher cleared first, as in 40250 Main) work.
- Image commands are base-texture quads with UVs (a .sub shares its parent
  texture); ImageInstance/ExpandedImageInstance OnRender and SetRenderingRect
  ported verbatim, so scale/rotation/rendering rect are drawn.
- CGraphicBase::GetColor / grp.GenerateColor ported (ThinBoard background).
- port.app_loop test, python_host_test app-loop checks, MT_TEST_MODE=python_ui.
- TODO: .fnt/CGraphicText font pipeline, ExpandedImage blend modes.

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

project/client_main.gd

@@ -35,6 +35,18 @@ func _ready() -> void:
 			printerr("%d check(s) failed" % fail)
 		get_tree().quit(1 if fail else 0)
 		return
+	# MT_TEST_MODE=python_ui：40250 system.py 的界面直接画在 Godot Canvas 上（PORT-PLAN 2V0-f），
+	# Logo → 登录阶段，可用鼠标键盘操作；app.Exit() 退出进程。
+	if OS.get_environment("MT_TEST_MODE") == "python_ui":
+		AssetPack.ensure()
+		var surface: Control = preload("res://python_ui_surface.gd").new()
+		surface.name = "PythonUISurface"
+		add_child(surface)
+		var err: String = surface.run_app()
+		if err != "":
+			printerr("python_ui: " + err)
+			get_tree().quit(1)
+		return
 	if OS.get_environment("MT_TEST_MODE") == "forest_render":
 		var forest := ForestMapRenderTest.new()
 		forest.name = "ForestMapRenderTest"