Address PR review: drop unused Windows detection and dispose xdotool Process

- Removed Windows branch from IsAutoSubmitModifierPressed (and the
  WindowsApplication helper). SimulatePaste/SimulateEnter have no
  Windows implementation yet, so detecting Ctrl there just caused a
  5s wait-for-release with no follow-up keystroke.
- Wrapped the Linux xdotool Process.Start calls in 'using' to dispose
  the returned Process handle.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: maraf

src/Neptuo.Productivity.SnippetManager.Avalonia/Navigator.cs

@@ -387,9 +387,9 @@ private static bool IsAutoSubmitModifierPressed()
         if (OperatingSystem.IsMacOS())
             return MacOSApplication.IsCommandKeyPressed();
 
-        if (OperatingSystem.IsWindows())
-            return WindowsApplication.IsCtrlKeyPressed();
-
+        // Other platforms don't yet have SimulatePaste/SimulateEnter implementations,
+        // so modifier detection stays disabled to avoid the wait-for-release stall
+        // with no keystroke follow-up.
         return false;
     }
 
@@ -475,7 +475,7 @@ private static void SimulatePaste()
         {
             try
             {
-                Process.Start(new ProcessStartInfo
+                using var process = Process.Start(new ProcessStartInfo
                 {
                     FileName = "xdotool",
                     Arguments = "key ctrl+v",
@@ -500,7 +500,7 @@ private static void SimulateEnter()
         {
             try
             {
-                Process.Start(new ProcessStartInfo
+                using var process = Process.Start(new ProcessStartInfo
                 {
                     FileName = "xdotool",
                     Arguments = "key Return",