refactor(P5b-5): 버튼 Click 핸들러 10개 → 커맨드 바인딩

상호작용 핸들러 중 '커맨드화 가능한' 순수 버튼 클릭을 전부 RelayCommand + Command 바인딩으로 전환.

- 상단바 5개(Settings/Register/Diagnose/ExportLog/ClearAll) + 폴더선택/취소/미리보기열기
  + 항목제거(CommandParameter={Binding}) + 폴더열기(CommandParameter={Binding RevealPath}).
- OnRemoveQueueItem→RemoveQueueItem(QueueItem?), OnOpenFolderClick→OpenFolderForPath(string?) 추출
  (sender.Tag 의존 제거 → CommandParameter).
- 검증: 빌드 0/0, 83 테스트 그린, publish 후 메인 창 크래시 없이 로드(언핸들드 로그 없음).
- 잔여 핸들러는 MVVM에서도 뷰/behavior 영역: 드래그앤드롭, SelectionChanged/ValueChanged,
  미리보기 마우스클릭, 탭·충돌 ToggleButton 그룹(IsChecked 상호배제), 복합 상태 ProcessQueue 버튼.

src/Everything2Everything.App/Views/MainWindow.xaml

@@ -161,7 +161,7 @@
                                              ToolTip="비워두면 원본 폴더 옆 서브폴더에 저장"/>
                                     <Button Grid.Column="1" Margin="8,0,0,0" Width="36"
                                             Content="…" Style="{StaticResource FsSecondaryButtonStyle}"
-                                            Click="OnPickOutputFolderClick"/>
+                                            Command="{Binding PickOutputFolderCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                                 </Grid>
                                 <TextBlock x:Name="OutputDestHint" Margin="0,6,0,0"
                                            Style="{StaticResource FsCaptionStyle}"
@@ -300,7 +300,7 @@
                                     <Button x:Name="CancelProcessingButton" Grid.Column="1"
                                             Content="취소" Padding="10,2"
                                             Style="{StaticResource FsSecondaryButtonStyle}"
-                                            Click="OnCancelProcessingClick"/>
+                                            Command="{Binding CancelProcessingCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                                 </Grid>
                             </StackPanel>
 
@@ -368,19 +368,19 @@
                         <StackPanel Grid.Column="1" Orientation="Horizontal">
                             <Button Content="⚙ 설정" Margin="0,0,8,0"
                                     Style="{StaticResource FsSecondaryButtonStyle}"
-                                    Click="OnSettingsClick"/>
+                                    Command="{Binding SettingsCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                             <Button Content="Register Menu" Margin="0,0,8,0"
                                     Style="{StaticResource FsSecondaryButtonStyle}"
-                                    Click="OnRegisterClick"/>
+                                    Command="{Binding RegisterCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                             <Button Content="Diagnose" Margin="0,0,8,0"
                                     Style="{StaticResource FsSecondaryButtonStyle}"
-                                    Click="OnDiagnoseClick"/>
+                                    Command="{Binding DiagnoseCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                             <Button Content="Export Log" Margin="0,0,8,0"
                                     Style="{StaticResource FsSecondaryButtonStyle}"
-                                    Click="OnExportLogClick"/>
+                                    Command="{Binding ExportLogCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                             <Button x:Name="ClearAllButton" Content="Clear All"
                                     Style="{StaticResource FsSecondaryButtonStyle}"
-                                    Click="OnClearAllClick"/>
+                                    Command="{Binding ClearAllCommand, RelativeSource={RelativeSource AncestorType=Window}}"/>
                         </StackPanel>
                     </Grid>
                 </Border>
@@ -500,8 +500,8 @@
                                                             VerticalAlignment="Center"
                                                             HorizontalAlignment="Right"
                                                             ToolTip="큐에서 제거"
-                                                            Click="OnRemoveQueueItem"
-                                                            Tag="{Binding}">
+                                                            Command="{Binding RemoveQueueItemCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                                            CommandParameter="{Binding}">
                                                         <Path Width="13" Height="13" Stretch="Uniform"
                                                               Stroke="{StaticResource FsTextTertiary}"
                                                               StrokeThickness="2"
@@ -618,8 +618,8 @@
                                                                     Background="Transparent"
                                                                     BorderThickness="0"
                                                                     Padding="6"
-                                                                    Click="OnOpenFolderClick"
-                                                                    Tag="{Binding RevealPath}"
+                                                                    Command="{Binding OpenFolderCommand, RelativeSource={RelativeSource AncestorType=Window}}"
+                                                                    CommandParameter="{Binding RevealPath}"
                                                                     ToolTip="출력 파일이 있는 폴더 열기">
                                                                 <Path Width="14" Height="14" Stretch="Uniform"
                                                                       Stroke="{StaticResource FsTextTertiary}"
@@ -779,7 +779,7 @@
 
                                     <Button Content="Open in Explorer" Margin="0,16,0,0"
                                             Style="{StaticResource FsSecondaryButtonStyle}"
-                                            Click="OnPreviewOpenFolder"
+                                            Command="{Binding PreviewOpenFolderCommand, RelativeSource={RelativeSource AncestorType=Window}}"
                                             HorizontalAlignment="Stretch"/>
                                 </StackPanel>
                             </Border>