Fix FloatingTabState crash + landscape layout on iPhone

Use UIDevice.userInterfaceIdiom instead of hSizeClass so large iPhones
in landscape keep the iPhone layout. Move tabState environmentObject to
the top-level Group so both layouts always have it in scope.

KisaniCal/ContentView.swift

@@ -61,14 +61,17 @@ struct ContentView: View {
         }
     }
 
+    private var isIPad: Bool { UIDevice.current.userInterfaceIdiom == .pad }
+
     var body: some View {
         Group {
-            if hSizeClass == .regular {
+            if isIPad {
                 iPadLayout()
             } else {
                 iPhoneLayout()
             }
         }
+        .environmentObject(tabState)
         .preferredColorScheme(preferredScheme)
         .fullScreenCover(isPresented: $showOnboarding) {
             OnboardingView(isPresented: $showOnboarding)
@@ -144,7 +147,6 @@ struct ContentView: View {
             .padding(.horizontal, 24)
             .padding(.bottom, 8)
         }
-        .environmentObject(tabState)
         .onAppear { UITabBar.appearance().isHidden = true }
     }