fix: add descriptive alt text to images on Learn page

[Sshadow84]

Description

Added descriptive alt text to images on the Learn page that previously had empty alt attributes.

Changes

• Added alt text to ETH logo image: "Ethereum diamond logo in blue and purple gradient"
• Added alt text to Web3 impact image: "Interconnected network nodes representing Web3 impact"
• Added alt text to wallet image: "Digital wallet interface with futuristic design elements"
• Added alt text to Layer 2 image: "Layer 2 network diagram showing scaling solutions"
• Added alt text to upgrade rings image: "Ethereum upgrade rings showing network improvements"
• Added alt text to DeFi image: "Decentralized finance icons and cryptocurrency symbols"

Why

Empty alt attributes make images inaccessible to screen reader users. This change improves accessibility compliance with WCAG guidelines.

Testing

• Verified images render correctly
• Alt text is descriptive and meaningful

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Lighthouse	7 paths audited Performance: 41 (🔴 down 14 from production) Accessibility: 94 (no change from production) Best Practices: 92 (🔴 down 8 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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