Refactor color management and UI components for consistency

- Updated color references in various widgets to use the new `opaquePrimary` color for better visual consistency.
- Refactored `ColorsManager` to improve color definitions and removed redundant color declarations.
- Enhanced UI elements across multiple dialogs and widgets to ensure a cohesive design language.

This change promotes maintainability and aligns with the updated color scheme.

lib/pages/routines/widgets/dialog_header.dart

@@ -18,7 +18,7 @@ class DialogHeader extends StatelessWidget {
           title,
           textAlign: TextAlign.center,
           style: Theme.of(context).textTheme.bodyMedium!.copyWith(
-                color: ColorsManager.primaryColorWithOpacity,
+                color: ColorsManager.opaquePrimary,
                 fontWeight: FontWeight.bold,
               ),
         ),