Fix port input crash: default port to 7147, use LostFocus binding

Changed default port from 5000 to 7147. Changed TextBox bindings
to UpdateSourceTrigger=LostFocus to prevent per-keystroke binding
updates that could crash on Android.

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

Author: sharpninja

src/RequestTracker.Android/Views/ConnectionDialogView.axaml

@@ -25,7 +25,7 @@
                 <!-- Host -->
                 <StackPanel Spacing="4">
                     <TextBlock Text="Host" FontSize="13" FontWeight="Medium"/>
-                    <TextBox Text="{Binding Host}"
+                    <TextBox Text="{Binding Host, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
                              Watermark="e.g. 192.168.1.100"
                              FontSize="16" Padding="10,8"
                              IsEnabled="{Binding !IsConnecting}"/>
@@ -34,8 +34,8 @@
                 <!-- Port -->
                 <StackPanel Spacing="4">
                     <TextBlock Text="Port" FontSize="13" FontWeight="Medium"/>
-                    <TextBox Text="{Binding Port}"
-                             Watermark="e.g. 5000"
+                    <TextBox Text="{Binding Port, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
+                             Watermark="e.g. 7147"
                              FontSize="16" Padding="10,8"
                              IsEnabled="{Binding !IsConnecting}"/>
                 </StackPanel>

src/RequestTracker.Core/ViewModels/ConnectionViewModel.cs

@@ -10,7 +10,7 @@ public partial class ConnectionViewModel : ViewModelBase
     private string _host = "192.168.1.100";
 
     [ObservableProperty]
-    private string _port = "5000";
+    private string _port = "7147";
 
     [ObservableProperty]
     private string _errorMessage = "";