Adds sticky bulk actions bar to category list view

[ronalfy]

This change introduces a sticky footer bar for category bulk actions in the categories list view, mirroring the functionality and appearance of the patterns screen.

Key updates include:

• Sticky Bulk Actions Bar: The bulk actions component is now rendered within a dedicated sticky container at the bottom of the viewport. This enhances accessibility and usability for bulk operations by keeping the controls visible while scrolling through categories.
• Layout Refinements: The scope of the form provider has been expanded to encompass the entire view, and the rendering logic for bulk actions has been adjusted to integrate seamlessly with the new sticky bar structure.
• Styling Adjustments: New CSS rules support the fixed bar layout, ensuring consistent presentation and an improved user experience.
• Code Readability: Various parts of the component, including state declarations and conditional logic, have been reformatted for better readability.