refactor(pricing): restructure pricing page, styles and tests

[vitormattos]

Superseded by #419, which preserves the same pricing scope with a clean branch history and avoids the failing commit metadata issues seen on this PR.

Original summary:

Summary

• extract WooCommerce pricing integration and page/view-model logic into dedicated support classes
• move pricing inline CSS to SCSS and encapsulate dynamic style generation
• add PHPUnit coverage and workflow for the pricing-related support layer

Scope

• Pricing page refactor
• Pricing-related support classes and tests
• PHPUnit infrastructure needed to validate this scope

Validation

• PHPUnit pricing/support suites passing locally
• Local static build passing