Material 3 theming

A serious application should define its visual language once rather than choosing arbitrary colors in every screen.

final theme = ThemeData(
  useMaterial3: true,
  colorScheme: ColorScheme.fromSeed(
    seedColor: const Color(0xFF6C5CE7),
  ),
);

• Centralize spacing and shape decisions.
• Use semantic color roles rather than hard-coded colors everywhere.
• Provide dark and light themes when appropriate.