refactor(P5b-7): 잔여 이벤트 핸들러 전부 커맨드/behavior로 — XAML 이벤트 핸들러 0개

Microsoft.Xaml.Behaviors.Wpf 도입. MainWindow.xaml에 직접 이벤트 핸들러(Click/SelectionChanged/Drop/
MouseUp 등) 0개 — 전부 선언적 바인딩·커맨드·InvokeCommandAction으로 전환.

- 드래그앤드롭(DragOver/DragLeave/Drop) → i:EventTrigger + InvokeCommandAction(PassEventArgsToCommand),
  HandleDragOver/HandleFilesDropped(DragEventArgs) 추출.
- 동적 포맷 콤보 SelectionChanged → OutputFormatChangedCommand(OnOutputFormatSelected).
- 큐·이력 행 PreviewMouseLeftButtonUp → QueueRow/PastRowCommand(MouseButtonEventArgs, IsInsideButton 가드
  보존 + e.OriginalSource.DataContext로 항목 해소).
- ProcessQueueButton Click → ProcessQueueCommand.
- 검증: 빌드 0/0, 83 테스트 그린, publish 후 메인 창 크래시 없이 로드(behaviors self-contained 정상).
  드래그앤드롭·행 미리보기·포맷 변경 실동작은 GUI 스모크 권장(비치명적 실패 모드).

src/Everything2Everything.App/Views/MainWindow.xaml

@@ -2,6 +2,7 @@
                  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                  xmlns:ui="http://schemas.lepo.co/wpfui/2022/xaml"
+                 xmlns:i="http://schemas.microsoft.com/xaml/behaviors"
                  Title="FormatShift Utility"
                  Icon="pack://application:,,,/Assets/app-icon.png"
                  Width="1280" Height="960"
@@ -11,9 +12,6 @@
                  WindowCornerPreference="Round"
                  WindowStartupLocation="CenterScreen"
                  AllowDrop="True"
-                 Drop="OnFilesDropped"
-                 DragOver="OnDragOver"
-                 DragLeave="OnDragLeave"
                  TextOptions.TextFormattingMode="Display"
                  UseLayoutRounding="True">
     <Window.Resources>
@@ -31,6 +29,18 @@
         <KeyBinding Key="F5" Command="{Binding RefreshCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
     </Window.InputBindings>
 
+    <i:Interaction.Triggers>
+        <i:EventTrigger EventName="DragOver">
+            <i:InvokeCommandAction Command="{Binding DragOverCommand, RelativeSource={RelativeSource AncestorType=Window}}" PassEventArgsToCommand="True"/>
+        </i:EventTrigger>
+        <i:EventTrigger EventName="DragLeave">
+            <i:InvokeCommandAction Command="{Binding DragLeaveCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
+        </i:EventTrigger>
+        <i:EventTrigger EventName="Drop">
+            <i:InvokeCommandAction Command="{Binding DropCommand, RelativeSource={RelativeSource AncestorType=Window}}" PassEventArgsToCommand="True"/>
+        </i:EventTrigger>
+    </i:Interaction.Triggers>
+
     <Grid Background="{StaticResource FsBgBase}">
         <Grid.RowDefinitions>
             <RowDefinition Height="32"/>
@@ -97,8 +107,13 @@
                                                    HorizontalAlignment="Center" VerticalAlignment="Center"/>
                                     </Border>
                                     <ComboBox x:Name="OutputFormatCombo" Grid.Column="1"
-                                              Margin="8,0,0,0" VerticalAlignment="Center"
-                                              SelectionChanged="OnOutputFormatChanged"/>
+                                              Margin="8,0,0,0" VerticalAlignment="Center">
+                                        <i:Interaction.Triggers>
+                                            <i:EventTrigger EventName="SelectionChanged">
+                                                <i:InvokeCommandAction Command="{Binding OutputFormatChangedCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
+                                            </i:EventTrigger>
+                                        </i:Interaction.Triggers>
+                                    </ComboBox>
                                 </Grid>
                                 <TextBlock x:Name="OutputFormatHint" Margin="0,6,0,0"
                                            Style="{StaticResource FsCaptionStyle}"
@@ -315,7 +330,7 @@
                                     Content="Idle — drop files to begin"
                                     Style="{StaticResource FsPrimaryButtonStyle}"
                                     IsEnabled="False"
-                                    Click="OnProcessQueueClick"/>
+                                    Command="{Binding ProcessQueueCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                         </StackPanel>
                     </Border>
                 </Grid>
@@ -456,9 +471,12 @@
                                                 Background="{StaticResource FsBgPanel}"
                                                 BorderBrush="{StaticResource FsBorderSubtle}"
                                                 BorderThickness="1"
-                                                Cursor="Hand"
-                                                PreviewMouseLeftButtonUp="OnQueueRowClick"
-                                                Tag="{Binding}">
+                                                Cursor="Hand">
+                                            <i:Interaction.Triggers>
+                                                <i:EventTrigger EventName="PreviewMouseLeftButtonUp">
+                                                    <i:InvokeCommandAction Command="{Binding QueueRowCommand, RelativeSource={RelativeSource AncestorType=Window}}" PassEventArgsToCommand="True"/>
+                                                </i:EventTrigger>
+                                            </i:Interaction.Triggers>
                                             <Grid>
                                                 <Grid.ColumnDefinitions>
                                                     <ColumnDefinition Width="2"/>
@@ -570,9 +588,12 @@
                                                     <Border BorderBrush="#0DFFFFFF"
                                                             BorderThickness="0,0,0,1" Padding="0,12"
                                                             Cursor="Hand"
-                                                            Background="Transparent"
-                                                            PreviewMouseLeftButtonUp="OnPastRowClick"
-                                                            Tag="{Binding}">
+                                                            Background="Transparent">
+                                                        <i:Interaction.Triggers>
+                                                            <i:EventTrigger EventName="PreviewMouseLeftButtonUp">
+                                                                <i:InvokeCommandAction Command="{Binding PastRowCommand, RelativeSource={RelativeSource AncestorType=Window}}" PassEventArgsToCommand="True"/>
+                                                            </i:EventTrigger>
+                                                        </i:Interaction.Triggers>
                                                         <Grid>
                                                             <Grid.ColumnDefinitions>
                                                                 <ColumnDefinition Width="40"/>