Style Prettyblock category tabs as buttons

[CySSoO]

Motivation

• Make the Prettyblock Category Tabs visually appear as pill buttons for clearer affordance and better visual integration with the theme.
• Provide dedicated CSS hooks so the tab appearance can be adjusted without altering markup elsewhere.

Description

• Add prettyblock-category-tabs__nav to the tab list and prettyblock-category-tabs__tab-link to each tab link in views/templates/hook/prettyblocks/prettyblock_category_tabs.tpl to expose styling hooks.
• Add styles in views/css/everblock.css to render tab links as rounded pill buttons with bordered, hover and active states using --bs-primary as the color source.
• Remove the default tab bottom border for the styled tab list and add spacing between pill buttons.

Testing

• No automated tests were run for this change.

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Codex Task