Prettyblock: remove iframe extra height and hide scrollbars

[CySSoO]

Motivation

• The Prettyblock iframe embeds showed an unwanted extra height and visible scrollbars causing layout issues.
• Add a consistent identifier to iframes to allow targeted styling and remove baseline gaps.
• Prevent scrollbars from appearing inside embedded videos/maps for a cleaner UI.
• Ensure both stock and custom iframe templates are covered.

Description

• Added everblock-prettyblock-iframe class to views/templates/hook/prettyblocks/prettyblock_iframe.tpl and views/templates/hook/prettyblocks/prettyblock_custom_iframe.tpl.
• Added scrolling="no" attribute to Prettyblock iframes to suppress internal scrollbars.
• Added CSS rules in views/css/everblock.css to set display: block, overflow: hidden, max-width: 100%, and hide scrollbars using scrollbar-width: none and ::-webkit-scrollbar.
• Applied the class to all iframe variants (YouTube, Vimeo, Dailymotion, Vidyard and custom iframe) to ensure consistent behavior.

Testing

• Attempted an automated Playwright screenshot of http://localhost/, which failed with net::ERR_EMPTY_RESPONSE.
• No other automated tests were run.

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Codex Task