refactor: update heading levels and improve markup in various components

[barbaraperic]

Description

• Changed heading levels from h5 to h4 in Footer.vue for consistency.
• Updated heading levels from h6 to h3 in Ecosystem.vue to enhance semantic structure.
• Modified Card.vue to replace Heading component with a span for the title, improving flexibility.
• Adjusted heading levels in KeyFeatures.vue from h5 to h4 for better hierarchy.
• Refactored HeroHome.vue to use a div instead of SectionHeader for the left template, enhancing layout control.
• Updated SectionHeader.vue to replace Heading with span for eyebrow text, improving accessibility.

These changes aim to improve the semantic structure and accessibility of the components while maintaining a consistent heading hierarchy across the application.

For reference, see Storacha Dogfooding Report.

Screenshot

Before

After