fix(app): hide native title bar text duplicating the toolbar pill

.windowToolbarStyle(.unifiedCompact(showsTitle: false)) — macOS's
unified toolbar renders the native title in the same row as a
.navigation-placed item, so setting both to the same collection/
document name showed it twice with the back button in between.
navigationTitle stays set for the Window menu, just not rendered here.

Outpost/OutpostApp.swift

@@ -35,6 +35,12 @@ struct OutpostApp: App {
                 #endif
         }
         #if os(macOS)
+        // On macOS's unified toolbar, the native title text renders in the
+        // same row as a `.navigation`-placed toolbar item — with both set to
+        // the same collection/document name, it visibly duplicated, with the
+        // system back button sandwiched between the two. `.navigationTitle`
+        // stays set (for the Window menu / Mission Control), just hidden here.
+        .windowToolbarStyle(.unifiedCompact(showsTitle: false))
         .commands {
             CommandGroup(replacing: .appInfo) {
                 Button("About Outpost") {