Fix wrong navigation styles on iPadOS

Gemini-iOS/PreferencesView.swift

@@ -23,6 +23,7 @@ struct PreferencesView: View {
             .insetOrGroupedListStyle()
             .navigationBarItems(trailing: doneButton)
         }
+        .navigationViewStyle(StackNavigationViewStyle())
         .onDisappear {
             Preferences.save()
         }

Gemini-iOS/TableOfContentsView.swift

@@ -46,6 +46,7 @@ struct TableOfContentsView: View {
                 close(nil)
             }))
         }
+        .navigationViewStyle(StackNavigationViewStyle())
     }
 }