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

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

Sources/Sst/HistoryView.swift

@@ -0,0 +1,9 @@
+import SstData
+import SstUI
+import SwiftUI
+
+// Temporary: replaced in Task 4.
+struct HistoryView: View {
+    @ObservedObject var list: HistoryViewModel
+    var body: some View { PaperBackground() }
+}