Redesign meetup detail page with card layout and carousel

[paulacianelli]

Summary

• Replaces the plain meetup detail layout with a breadcrumb nav, hero section, and two-column card grid (host + speakers on the left, talk carousel on the right)
• Adds a vanilla JS carousel using scroll-snap + IntersectionObserver with prev/next buttons and a slide counter
• Updates the meetup list to use Spanish month abbreviations and adds year anchor IDs for breadcrumb deep-links
• Fixes accessible breadcrumb separators (aria-hidden on inner <span>, not <li>) and adds speaker.photo fallback in carousel slide avatars

Test plan

• Visit a meetup detail page and verify hero, host card, speakers card, and talk carousel render correctly
• Verify carousel prev/next buttons navigate between talks and the counter updates
• Verify breadcrumb links navigate to /#meetups and /#meetups-{year}
• Check a speaker with only photo (no github) shows their avatar in both the speakers card and carousel slide
• Verify the meetup list shows Spanish month abbreviations (e.g. "06 ABR")
• Test on mobile (≤980px) — layout should stack to single column

[github-actions]

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