refactor: add color assets and update UI components

Mayday/ContentView.swift

@@ -1,7 +1,7 @@
 import SwiftUI
 
 struct ContentView: View {
-    @EnvironmentObject var authViewModel: AuthViewModel
+    @Environment(AuthViewModel.self) private var authViewModel
 
     var body: some View {
         Group {
@@ -19,3 +19,8 @@ struct ContentView: View {
         }
     }
 }
+
+#Preview {
+    ContentView()
+        .environment(AuthViewModel())
+}