chore(unity): 固定Unity CLI Loop本地包并移除UnitySkills依赖

Client/Packages/io.github.hatayama.uloopmcp/Editor/Utils/ProcessStartHelper.cs

@@ -0,0 +1,27 @@
+using System.ComponentModel;
+using System.Diagnostics;
+
+namespace io.github.hatayama.uLoopMCP
+{
+    public static class ProcessStartHelper
+    {
+        // NativeErrorCode 2 (ERROR_FILE_NOT_FOUND) and 3 (ERROR_PATH_NOT_FOUND) on Windows
+        // map to ENOENT on POSIX; other Win32Exception causes (e.g. permission denied) should
+        // propagate so callers fail fast instead of silently treating them as "not installed".
+        private const int ERROR_FILE_NOT_FOUND = 2;
+        private const int ERROR_PATH_NOT_FOUND = 3;
+
+        public static Process TryStart(ProcessStartInfo startInfo)
+        {
+            try
+            {
+                return Process.Start(startInfo);
+            }
+            catch (Win32Exception ex) when (ex.NativeErrorCode == ERROR_FILE_NOT_FOUND
+                                            || ex.NativeErrorCode == ERROR_PATH_NOT_FOUND)
+            {
+                return null;
+            }
+        }
+    }
+}