feat(python): 在 app 进程里起 40250 脚本层（2P step 4，macOS）

移植 UserInterface/RunMainScript 到 platform/ScriptLib/PythonBoot：40250 把
CPythonLauncher 放在 Main() 的栈上，这里进程归 Godot，launcher 必须活过创建它的
那次调用，所以拆成 Start / RunMainScript / RunLine / Stop。37 个模块初始化函数里
只调已移植的 initpack()，system.py 因此仍停在第一个 import。

脚本报错能传回 GDScript，靠的是 platform/EterBase/Debug.cpp 实现 LogBox/LogBoxf：
ScriptLib 的 Traceback() 在 PyErr_Fetch 之后只剩这一条路，LastLogBoxMessage()
（platform/EterBase/LogBox.h）是 traceback 唯一幸存的地方。

GDScript 侧新增 Metin2PythonHost（python_host_node.{h,cpp}）——唯一同时认识
godot-cpp 和 port 树的单元，PythonBoot 保持 godot-free。检查脚本
python_host_check.gd 分两段：解释器 + 标准库那段不需要 40250 的 pack，哪个平台都
能跑；system.py 那段需要 pack，没有就跳过。桌面入口 python_host_test.gd，真机入口
MT_TEST_MODE=python（导出模板不接受 --script）。

验证（macOS）：标准库可 import、codec 注册表可用、sys.path 非空，system.py 停在和
ctest port.python_launcher 完全相同的 ImportError: No module named app；
ctest 27/27。Android/iOS 进程内未做，正式启动路径仍不起解释器（2V0）。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/src/platform/ScriptLib/PythonBoot.cpp

@@ -0,0 +1,150 @@
+// See PythonBoot.h. The sequence is 40250 UserInterface.cpp:241-352 (RunMainScript) and 419-434 (Main),
+// split so the launcher can outlive the call that creates it.
+#include "ScriptLib/StdAfx.h"
+#include "ScriptLib/PythonLauncher.h"
+#include "UserInterface/StdAfx.h" // initpack and the rest of the module initializer list
+#include "PythonBoot.h"
+#include "PythonHost.h"
+#include "../EterBase/LogBox.h"
+
+#include <memory>
+
+namespace
+{
+// 40250 has this on Main()'s stack. CPythonLauncher is a CSingleton, so there is still only ever one.
+std::unique_ptr<CPythonLauncher> g_launcher;
+
+bool fail(std::string* error, const std::string& text)
+{
+	if (error)
+		*error = text;
+	return false;
+}
+}
+
+namespace PythonBoot
+{
+
+bool IsRunning()
+{
+	return g_launcher != nullptr;
+}
+
+bool Start(const char* stdlib_path, std::string* error)
+{
+	if (g_launcher)
+		return true;
+
+	const std::string stdlib = (stdlib_path && *stdlib_path) ? stdlib_path : PythonHost::DefaultStdLibPath();
+	if (stdlib.empty())
+		return fail(error, "no Python standard library path (Metin2Python.stdlib_path / $MT_PYTHON_STDLIB)");
+
+	// The flags have to be set before the interpreter starts, i.e. before the constructor below.
+	PythonHost::Configure();
+
+	g_launcher = std::make_unique<CPythonLauncher>(); // Py_Initialize
+	if (!g_launcher->Create())
+	{
+		Stop();
+		return fail(error, "CPythonLauncher::Create failed");
+	}
+
+	std::string stdlib_error;
+	if (!PythonHost::InstallStdLib(stdlib.c_str(), &stdlib_error))
+	{
+		Stop();
+		return fail(error, "InstallStdLib(" + stdlib + "): " + stdlib_error);
+	}
+	return true;
+}
+
+// 40250: RunMainScript
+bool RunMainScript(const char* lpCmdLine, std::string* error)
+{
+	if (!g_launcher)
+		return fail(error, "PythonBoot::Start has not run");
+
+	CPythonLauncher& pyLauncher = *g_launcher;
+
+	// The module initializers, in 40250's order. Everything after initpack (initdbg, initime, initgrp,
+	// initgrpImage, initgrpText, initwndMgr, initudp, initapp, ... initServerStateChecker) is a 2V slice:
+	// system.py stops at the first import of one of them, today `app`.
+	initpack();
+
+	ClearLogBoxMessage();
+
+	NANOBEGIN
+
+	// RegisterDebugFlag
+	{
+		std::string stRegisterDebugFlag;
+
+#ifdef _DISTRIBUTE
+		stRegisterDebugFlag ="__DEBUG__ = 0";
+#else
+		stRegisterDebugFlag ="__DEBUG__ = 1";
+#endif
+
+		if (!pyLauncher.RunLine(stRegisterDebugFlag.c_str()))
+		{
+			TraceError("RegisterDebugFlag Error");
+			return fail(error, "RegisterDebugFlag Error: " + LastLogBoxMessage());
+		}
+	}
+
+	// RegisterCommandLine.
+	// PORT: the "-cs"/"-ncs" auto-login argument is passed through unchanged. Decoding it needs
+	// EterBase/Utils.cpp SplitLine and EterLib/Util.cpp base64_decode, which are declared but not ported
+	// yet; they belong to the login track (批次 2V1) and nothing in this host passes -cs today.
+	{
+		std::string stRegisterCmdLine;
+
+		std::string stCmdLine = lpCmdLine ? lpCmdLine : "";
+
+		stRegisterCmdLine ="__COMMAND_LINE__ = ";
+		stRegisterCmdLine+='"';
+		stRegisterCmdLine+=stCmdLine;
+		stRegisterCmdLine+='"';
+
+		const CHAR* c_szRegisterCmdLine=stRegisterCmdLine.c_str();
+		if (!pyLauncher.RunLine(c_szRegisterCmdLine))
+		{
+			TraceError("RegisterCommandLine Error");
+			return fail(error, "RegisterCommandLine Error: " + LastLogBoxMessage());
+		}
+	}
+	// PORT: 40250 also honours "--pause-before-create-window" here with system("pause") and the XTrap
+	// init check. Neither exists on this platform (no console to pause, no XTrap), so only the RunFile
+	// is kept.
+	{
+		if (!pyLauncher.RunFile("system.py"))
+		{
+			TraceError("RunMain Error");
+			return fail(error, "RunMain Error: " + LastLogBoxMessage());
+		}
+	}
+
+	NANOEND
+	return true;
+}
+
+bool RunLine(const char* source, std::string* error)
+{
+	if (!g_launcher)
+		return fail(error, "PythonBoot::Start has not run");
+
+	ClearLogBoxMessage();
+	if (!g_launcher->RunLine(source ? source : ""))
+		return fail(error, LastLogBoxMessage());
+	return true;
+}
+
+void Stop()
+{
+	if (!g_launcher)
+		return;
+	g_launcher->Clear(); // Main() calls Clear() explicitly before the launcher leaves scope
+	g_launcher.reset();
+}
+
+}