초기 커밋: SheetMe 서식생성기 (P0~P5 완료 상태)

레거시 서식생성기(VB.NET WinForms) 대체용 C#/.NET 10 WPF 디자이너.
기준선: 실DB 활성 디자인 1,271건 왕복 의미론 diff 0 / 예외 0, 단위 테스트 49/49.

이 커밋에 함께 포함된 자격증명 분리:
- appsettings.json 을 __HOST__/__PASSWORD__ 플레이스홀더로 전환
- 실접속 정보는 appsettings.Development.json 으로 분리(.gitignore 제외,
  csproj Debug 조건부 복사라 Release 산출물에 실리지 않음)
- ConfigLoader 를 환경변수 > Development > appsettings 순 레이어링으로 변경,
  미치환 플레이스홀더는 '미설정'으로 간주

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/SheetMe.Designer/Views/DesignerCanvasView.xaml

@@ -0,0 +1,73 @@
+<UserControl x:Class="SheetMe.Designer.Views.DesignerCanvasView"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             xmlns:b="http://schemas.microsoft.com/xaml/behaviors"
+             xmlns:vm="clr-namespace:SheetMe.Designer.ViewModels"
+             xmlns:v="clr-namespace:SheetMe.Designer.Views"
+             xmlns:bh="clr-namespace:SheetMe.Designer.Behaviors"
+             mc:Ignorable="d"
+             d:DataContext="{d:DesignInstance vm:DesignerViewModel}"
+             Focusable="True" FocusVisualStyle="{x:Null}"
+             PreviewKeyDown="OnCanvasPreviewKeyDown" PreviewKeyUp="OnCanvasPreviewKeyUp">
+
+    <!-- 키보드 단축키(텍스트 입력 보호 포함) -->
+    <b:Interaction.Behaviors>
+        <bh:CanvasKeyboardBehavior/>
+    </b:Interaction.Behaviors>
+
+    <!-- 디자인 캔버스: 스크롤 + 줌(LayoutTransform) 월드. 입력은 World 1곳에서 수신 -->
+    <ScrollViewer x:Name="Scroll"
+                  HorizontalScrollBarVisibility="Auto"
+                  VerticalScrollBarVisibility="Auto"
+                  Background="{DynamicResource B.CanvasBg}"
+                  Focusable="False"
+                  PreviewMouseWheel="OnPreviewMouseWheel"
+                  PreviewMouseLeftButtonDown="OnPanMouseDown"
+                  PreviewMouseMove="OnPanMouseMove"
+                  PreviewMouseLeftButtonUp="OnPanMouseUp"
+                  LostMouseCapture="OnPanLostCapture">
+        <Border Padding="24">
+            <Grid x:Name="World"
+                  Background="Transparent"
+                  HorizontalAlignment="Left" VerticalAlignment="Top"
+                  Width="{Binding WorldWidth}" Height="{Binding WorldHeight}">
+                <Grid.LayoutTransform>
+                    <ScaleTransform ScaleX="{Binding Zoom}" ScaleY="{Binding Zoom}"/>
+                </Grid.LayoutTransform>
+
+                <b:Interaction.Behaviors>
+                    <bh:CanvasMouseBehavior/>
+                    <bh:CanvasDropBehavior/>
+                </b:Interaction.Behaviors>
+
+                <!-- 층1: 페이지 스택 -->
+                <ItemsControl ItemsSource="{Binding Pages}">
+                    <ItemsControl.ItemsPanel>
+                        <ItemsPanelTemplate>
+                            <Canvas/>
+                        </ItemsPanelTemplate>
+                    </ItemsControl.ItemsPanel>
+                    <ItemsControl.ItemContainerStyle>
+                        <Style TargetType="ContentPresenter">
+                            <Setter Property="Canvas.Left" Value="0"/>
+                            <Setter Property="Canvas.Top" Value="{Binding OffsetY}"/>
+                        </Style>
+                    </ItemsControl.ItemContainerStyle>
+                    <ItemsControl.ItemTemplate>
+                        <DataTemplate>
+                            <v:PageView/>
+                        </DataTemplate>
+                    </ItemsControl.ItemTemplate>
+                </ItemsControl>
+
+                <!-- 층2: 선택/마퀴/가이드 오버레이 (표시 전용) -->
+                <v:SelectionOverlayView DataContext="{Binding Overlay}"/>
+
+                <!-- 층3: 인라인 텍스트 에디터 (더블클릭 시 코드비하인드가 배치) -->
+                <Canvas x:Name="EditorLayer"/>
+            </Grid>
+        </Border>
+    </ScrollViewer>
+</UserControl>