refactor: add color assets and update UI components

Mayday/Views/UIKit/AppBackground.swift

@@ -4,7 +4,7 @@ struct AppBackgroundModifier: ViewModifier {
     func body(content: Content) -> some View {
         content.background(
             LinearGradient(
-                colors: [Color(.systemGroupedBackground), Color.red.opacity(0.08)],
+                colors: [Color(.systemGroupedBackground), Color.brand.opacity(0.08)],
                 startPoint: .top,
                 endPoint: .bottom
             )

Mayday/Views/UIKit/AppColors.swift

@@ -0,0 +1,15 @@
+import SwiftUI
+
+extension Color {
+    static let brand = Color("Brand")
+    static let success = Color("Success")
+    static let warning = Color("Warning")
+    static let info = Color("Info")
+}
+
+extension ShapeStyle where Self == Color {
+    static var brand: Color { .brand }
+    static var success: Color { .success }
+    static var warning: Color { .warning }
+    static var info: Color { .info }
+}

Mayday/Views/UIKit/AppSecureField.swift

@@ -23,3 +23,8 @@ struct AppSecureField: View {
         )
     }
 }
+
+#Preview {
+    AppSecureField(title: "Password", icon: "lock.fill", text: .constant(""))
+        .padding()
+}

Mayday/Views/UIKit/AppTextField.swift

@@ -23,3 +23,8 @@ struct AppTextField: View {
         )
     }
 }
+
+#Preview {
+    AppTextField(title: "Email", icon: "envelope.fill", text: .constant("user@example.com"))
+        .padding()
+}

Mayday/Views/UIKit/NotificationIconView.swift

@@ -17,10 +17,10 @@ enum NotificationSeverity: String {
 
     var color: Color {
         switch self {
-        case .critical: return .red
-        case .warning:  return .orange
-        case .info:     return .blue
-        case .success:  return .green
+        case .critical: return .brand
+        case .warning:  return .warning
+        case .info:     return .info
+        case .success:  return .success
         }
     }
 
@@ -45,3 +45,13 @@ struct NotificationIconView: View {
         }
     }
 }
+
+#Preview {
+    HStack(spacing: 16) {
+        NotificationIconView(severity: .critical, isActive: true)
+        NotificationIconView(severity: .warning, isActive: false)
+        NotificationIconView(severity: .info, isActive: false)
+        NotificationIconView(severity: .success, isActive: false)
+    }
+    .padding()
+}