Improve uploader client connection and diagnostics

clients/photobooth-uploader/PhotoboothUploader/MainWindow.axaml

@@ -30,6 +30,7 @@
                 <TextBlock Text="Upload-Ordner" FontWeight="SemiBold" />
                 <TextBlock x:Name="FolderText" Text="Noch nicht ausgewählt." TextWrapping="Wrap" />
                 <Button x:Name="PickFolderButton" Content="Ordner auswählen" Click="PickFolderButton_Click" IsEnabled="False" />
+                <Button x:Name="TestUploadButton" Content="Test-Upload senden" Click="TestUploadButton_Click" IsEnabled="False" />
             </StackPanel>
 
             <ToggleSwitch x:Name="QuietToggle" Content="Ruhiger Modus (nur Fehler anzeigen)" />
@@ -41,6 +42,17 @@
                     <TextBlock Text="Status" FontWeight="SemiBold" />
                     <TextBlock x:Name="StatusText" Text="Nicht verbunden." TextWrapping="Wrap" />
                     <TextBlock x:Name="LastUploadText" Text="Letzter Upload: —" />
+                    <TextBlock x:Name="QueueStatusText" Text="Warteschlange: 0 · Läuft: 0 · Fehlgeschlagen: 0" />
+                </StackPanel>
+            </Border>
+
+            <Border Background="#1F000000" Padding="12" CornerRadius="8">
+                <StackPanel Spacing="6">
+                    <TextBlock Text="Details" FontWeight="SemiBold" />
+                    <TextBlock x:Name="EventNameText" Text="Event: —" TextWrapping="Wrap" />
+                    <TextBlock x:Name="BaseUrlText" Text="Basis-URL: —" TextWrapping="Wrap" />
+                    <TextBlock x:Name="VersionText" Text="App-Version: —" />
+                    <TextBlock x:Name="LastErrorText" Text="Letzter Fehler: —" TextWrapping="Wrap" />
                 </StackPanel>
             </Border>