feat: ContentHero design update

[wackerow]

Description

Updates ContentHero according to new /what-is-ethereum designs

• Removes bg gradient, enlarged font size and increase font weight
• Updated image handling to be more robust with width/height properties
• Aside: switched to png for translatathon hero to comply; about the same size for a 3x version, and offers blurred loading state with sizing dimensions

[netlify]

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Lighthouse	7 paths audited Performance: 56 (🟢 up 5 from production) Accessibility: 94 (no change from production) Best Practices: 92 (no change from production) SEO: 99 (no change from production) PWA: 59 (no change from production) View the detailed breakdown and full score reports

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