Refine newsletter prettyblock styling to match mockup

[CySSoO]

Motivation

• Align the prettyblock newsletter block with the provided visual mockup by adjusting spacing, typography and layout.
• Remove hard-coded colors and move all color/styling control to the block configuration so theming is driven from settings.
• Make the newsletter layout more centered and wide to improve presentation on desktop while keeping responsive behavior.

Description

• Added multiple design configuration fields for the everblock_newsletter block in src/Service/EverblockPrettyBlocks.php (examples: subtitle_color, legal_text_color, message_*, input_*, button_*).
• Exposed CSS custom properties from the template views/templates/hook/prettyblocks/prettyblock_newsletter.tpl by writing block settings into inline --prettyblock-* variables so colors come from configuration.
• Updated views/css/everblock.css to rely on the new CSS variables with safe fallbacks, adjusted layout (centered inner container, wider max-width, updated paddings, rounded radius), and refined input/button/title/subtitle styles to match the mockup.
• Added conservative defaults and fallbacks in CSS so the block degrades gracefully if settings are not provided.

Testing

• No automated tests were run.

---

Codex Task