Refactor: Create `BuildContext` extension for `Theme` to reduce boilerplate

[ZhuchkaTriplesix]

Description

There are over 170 instances of Theme.of(context).colorScheme or Theme.of(context) scattered throughout the UI layer.

Why is this a problem?

Constantly repeating Theme.of(context) leads to visual noise and boilerplate in the build methods, making widget code harder to read.

Proposed Solution

Create a centralized BuildContext extension to streamline this framework boilerplate.

Implementation:

extension BuildContextThemeExt on BuildContext {
  ThemeData get theme => Theme.of(this);
  ColorScheme get colors => Theme.of(this).colorScheme;
}

This allows reducing Theme.of(context).colorScheme.primary down to a much cleaner context.colors.primary globally.