fix(client): 开机自启隐藏窗口在原生 runner 层跳过首帧 Show()(1.0.29)

1.0.28 的 Dart hide() 早于 Flutter Windows runner 首帧回调的 Show(),被覆盖,
窗口仍弹出。改在 flutter_window.cpp 检测命令行 --autostart 时不注册首帧 Show()
回调,窗口(WS_OVERLAPPEDWINDOW 无 WS_VISIBLE)保持隐藏;Dart hide() 保留以同步
window_manager 状态。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/windows/installer/pangolin.iss

@@ -3,7 +3,7 @@
 ; 前置: 先在 client/ 跑 `flutter build windows`(Release),产物在
 ;       ..\..\build\windows\x64\runner\Release
 #define MyAppName "穿山甲 Pangolin"
-#define MyAppVersion "1.0.28"
+#define MyAppVersion "1.0.29"
 #define MyAppPublisher "Pangolin"
 #define MyAppExeName "pangolin_vpn.exe"
 #define BuildDir "..\..\build\windows\x64\runner\Release"