Fix/appbartheme compat

[ctenuta]

What was changed

• Updated AppBarTheme.of(context) type to AppBarThemeData.
• Replaced textTheme.bodyText2 with textTheme.bodyMedium.
• Removed deprecated accentColor, now using colorScheme.copyWith(secondary: ...).
• Enabled useMaterial3: true in ThemeData.

Why

Starting with Flutter 3.32+ (Material 3):

• accentColor has been removed.
• Several TextTheme getters were renamed.
• AppBarTheme.of now returns AppBarThemeData.

Without these changes the package fails to compile on the latest Flutter stable.

How it was tested

• Built and tested on Flutter 3.32.8 (stable).
• flutter build appbundle completed successfully.
• Verified AppBar and text styling still follow the theme.