Add explicit image dimensions for page cover and Instagram thumbnails

[CySSoO]

Motivation

• Reduce cumulative layout shift (CLS) by ensuring images render with explicit width and height attributes.
• The page cover (hero) and Instagram carousel thumbnails previously lacked dimensions, causing layout shifts that hurt Core Web Vitals and SEO.

Description

• Use EverblockPage::getCoverImageData in controllers/front/page.php and expose everblock_page_image_data (URL, width, height, alt) to templates.
• Render the page cover <img> with width and height in views/templates/front/page.tpl using {$everblock_page_image_data.width} and {$everblock_page_image_data.height}.
• When fetching Instagram posts in src/Service/EverblockTools.php, compute image dimensions with getimagesize() (with a fallback size) and include width/height in each cached item.
• Output width and height attributes for Instagram thumbnails in views/templates/hook/instagram.tpl to stabilize the carousel layout.

Testing

• No automated tests were executed for this change in the current environment.

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Codex Task