Disable resizing in `ConvertWindow`, adjust window size behavior, and set dynamic title initialization for macOS views.

src/PicView.Avalonia.MacOS/Views/ConvertWindow.axaml

@@ -1,5 +1,8 @@
 <Window
-    Title="ConvertWindow"
+    CanResize="False"
+    ExtendClientAreaChromeHints="SystemChrome"
+    ExtendClientAreaTitleBarHeightHint="-1"
+    SizeToContent="WidthAndHeight"
     d:DesignHeight="450"
     d:DesignWidth="800"
     mc:Ignorable="d"

src/PicView.Avalonia.MacOS/Views/ConvertWindow.axaml.cs

@@ -1,4 +1,6 @@
 using Avalonia.Controls;
+using PicView.Avalonia.UI;
+using PicView.Core.Localization;
 
 namespace PicView.Avalonia.MacOS.Views;
 
@@ -7,5 +9,6 @@ public partial class ConvertWindow : Window
     public ConvertWindow()
     {
         InitializeComponent();
+        GenericWindowHelper.GenericWindowInitialize(this, TranslationManager.Translation.ConvertTo + " - PicView");
     }
 }