feat(app): wire up appearance setting and app menu commands

AppAppearance (System/Light/Dark) applies via NSApp.appearance directly
rather than .preferredColorScheme(nil) — the latter doesn't reliably
reset a macOS window back to "follow system" after an explicit
override. App menu gets About/Log Out commands and the About/Keyboard
Shortcuts/Preferences windows registered as scenes.

Outpost/OutpostApp.swift

@@ -6,27 +6,83 @@
 //
 
 import SwiftUI
-import SwiftData
+
+#if os(macOS)
+import AppKit
+#endif
 
 @main
 struct OutpostApp: App {
-    var sharedModelContainer: ModelContainer = {
-        let schema = Schema([
-            Item.self,
-        ])
-        let modelConfiguration = ModelConfiguration(schema: schema, isStoredInMemoryOnly: false)
+    @State private var session = SessionStore()
+    @AppStorage("outpost.appearance") private var appearance: AppAppearance = .system
 
-        do {
-            return try ModelContainer(for: schema, configurations: [modelConfiguration])
-        } catch {
-            fatalError("Could not create ModelContainer: \(error)")
-        }
-    }()
+    #if os(macOS)
+    @Environment(\.openWindow) private var openWindow
+    @State private var isShowingLogoutConfirmation = false
+    #endif
 
     var body: some Scene {
         WindowGroup {
-            ContentView()
+            RootView()
+                .environment(session)
+                #if os(iOS)
+                .preferredColorScheme(appearance.colorScheme)
+                #endif
+                #if os(macOS)
+                .onAppear { applyMacAppearance() }
+                .onChange(of: appearance) { _, _ in applyMacAppearance() }
+                .logoutConfirmationDialog(isPresented: $isShowingLogoutConfirmation, session: session)
+                #endif
         }
-        .modelContainer(sharedModelContainer)
+        #if os(macOS)
+        .commands {
+            CommandGroup(replacing: .appInfo) {
+                Button("About Outpost") {
+                    openWindow(id: "about")
                 }
             }
+            CommandGroup(after: .appSettings) {
+                Divider()
+                Button("Log Out…") {
+                    isShowingLogoutConfirmation = true
+                }
+                .disabled(!session.isSignedIn)
+            }
+        }
+        #endif
+
+        #if os(macOS)
+        Window("About Outpost", id: "about") {
+            AboutView()
+        }
+        .windowResizability(.contentSize)
+
+        Window("Keyboard Shortcuts", id: "keyboard-shortcuts") {
+            KeyboardShortcutsView()
+        }
+        .windowResizability(.contentSize)
+
+        Settings {
+            PreferencesView()
+                .environment(session)
+        }
+        #endif
+    }
+
+    #if os(macOS)
+    /// `.preferredColorScheme(nil)` doesn't reliably reset the window's real
+    /// `NSAppearance` back to "follow system" after an explicit override — this
+    /// sets the actual AppKit-level appearance directly instead, which every
+    /// window (present and future) inherits.
+    private func applyMacAppearance() {
+        switch appearance {
+        case .system:
+            NSApp.appearance = nil
+        case .light:
+            NSApp.appearance = NSAppearance(named: .aqua)
+        case .dark:
+            NSApp.appearance = NSAppearance(named: .darkAqua)
+        }
+    }
+    #endif
+}

Outpost/Support/AppAppearance.swift

@@ -0,0 +1,23 @@
+import SwiftUI
+
+enum AppAppearance: String, CaseIterable, Identifiable {
+    case system, light, dark
+
+    var id: String { rawValue }
+
+    var label: String {
+        switch self {
+        case .system: return "System"
+        case .light: return "Light"
+        case .dark: return "Dark"
+        }
+    }
+
+    var colorScheme: ColorScheme? {
+        switch self {
+        case .system: return nil
+        case .light: return .light
+        case .dark: return .dark
+        }
+    }
+}