feat: add deck, sidebar with controls and the main window layout

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Sources/Sst/MainWindow.swift

@@ -1,23 +1,29 @@
-import SwiftUI
 import SstUI
+import SwiftUI
 
-/// Placeholder shell; phase 5 replaces the content with the deck, history and dictionary.
 struct MainWindow: View {
     @EnvironmentObject private var model: AppModel
 
     var body: some View {
         ZStack {
             BrushedBackground().ignoresSafeArea()
-            VStack(alignment: .leading, spacing: Layout.panelGap) {
-                SilkLabel(AppIdentity.brandCaption)
-                Text(model.statusLine)
-                    .textStyle(Typography.reading)
-                    .foregroundStyle(Palette.inkPrimary)
-                    .padding(Layout.panelPadding)
-                    .frame(maxWidth: .infinity, alignment: .leading)
-                    .background(PanelBackground())
+            HStack(spacing: 0) {
+                Sidebar()
+                VStack(spacing: Layout.panelGap) {
+                    DeckView()
+                    switch model.section {
+                    case .transcripts: HistoryView(list: model.historyList)
+                    case .dictionary: DictionaryView(list: model.dictionaryList)
+                    }
+                }
+                .padding(Layout.panelPadding)
             }
-            .padding(Layout.panelPadding)
+        }
+        .confirmationDialog(Strings.clearHistoryConfirm, isPresented: $model.confirmingClearHistory) {
+            Button(Strings.erase, role: .destructive) { model.clearHistory() }
+            Button(Strings.cancel, role: .cancel) {}
+        } message: {
+            Text(Strings.clearHistoryDetail)
         }
     }
 }