Build passport-style identity app shell

Sources/App/IDPGlobalApp.swift

@@ -0,0 +1,63 @@
+import SwiftUI
+
+@main
+struct IDPGlobalApp: App {
+    @StateObject private var model = AppViewModel()
+
+    var body: some Scene {
+        WindowGroup {
+            RootView(model: model)
+                .tint(Color(red: 0.12, green: 0.40, blue: 0.31))
+                .task {
+                    await model.bootstrap()
+                }
+                .alert("Something went wrong", isPresented: errorPresented) {
+                    Button("OK") {
+                        model.errorMessage = nil
+                    }
+                } message: {
+                    Text(model.errorMessage ?? "")
+                }
+        }
+        #if os(macOS)
+        .defaultSize(width: 1380, height: 920)
+        #endif
+    }
+
+    private var errorPresented: Binding<Bool> {
+        Binding(
+            get: { model.errorMessage != nil },
+            set: { isPresented in
+                if !isPresented {
+                    model.errorMessage = nil
+                }
+            }
+        )
+    }
+}
+
+private struct RootView: View {
+    @ObservedObject var model: AppViewModel
+
+    var body: some View {
+        Group {
+            if model.session == nil {
+                LoginRootView(model: model)
+            } else {
+                HomeRootView(model: model)
+            }
+        }
+        .background(
+            LinearGradient(
+                colors: [
+                    Color(red: 0.96, green: 0.97, blue: 0.94),
+                    Color(red: 0.89, green: 0.94, blue: 0.92),
+                    Color(red: 0.94, green: 0.91, blue: 0.84)
+                ],
+                startPoint: .topLeading,
+                endPoint: .bottomTrailing
+            )
+            .ignoresSafeArea()
+        )
+    }
+}