Refactor: Use DesignInterface for Hyvä Theme Detection in ProductGalleryHelper

[itaymesh]

Description:

Overview

This PR updates the ProductGalleryHelper::isHyvaThemeEnabled() method to use DesignInterface instead of ThemeProvider, ensuring accurate detection of Hyvä-based themes, including child themes.

Changes:

• Replaced ThemeProvider with DesignInterface to align with \Hyva\Theme\Service\CurrentTheme::isHyva().
• Updated isHyvaThemeEnabled() to check parent themes recursively for better Hyvä theme detection.
• Injected DesignInterface via constructor to follow Magento's best practices.

Why This Change?

• Ensures compatibility with Hyvä child themes.
• Matches Hyvä’s official approach to theme detection.
• Reduces direct reliance on ThemeProvider and ScopeConfigInterface for theme resolution.

Notes:

• This change does not affect existing functionality beyond improving Hyvä theme detection.

• No other parts of the class were refactored to maintain scope.