Limit Prettyblocks to first guides listing page

[CySSoO]

Motivation

• Allow editors to add content (top/bottom zones) that appears only on the first guides listing page and provide a flag for template-level customizations (e.g. header/footer text on page 1).

Description

• Compute $showPageOneBlocks as isPrettyBlocksEnabled && $currentPage === 1 in controllers/front/pages.php.
• Use $showPageOneBlocks to set everblock_prettyblocks_enabled and the top/bottom zone names passed to Smarty.
• Expose everblock_is_first_page boolean to the template for future use.
• Changes are limited to controllers/front/pages.php template variable assignments.

Testing

• No automated tests were executed for this change.

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Codex Task