[codex] fix Twitter card meta attributes

[Sean-Kenneth-Doherty]

Summary

• Change the shared layout Twitter Card tags from property="twitter:*" to name="twitter:*".
• Add og:image:alt and twitter:image:alt metadata with a reusable imageAlt layout prop.
• Align the Twitter creator/site handle with the public @1stContribution handle used elsewhere in the site.
• Add a 1200x630 PNG social card image and use it as the default og:image / twitter:image URL.
• Shorten the home page metadata title so the rendered title, Open Graph title, and Twitter title stay under common SEO title-length thresholds.

Why

X/Twitter Cards documentation shows card properties as meta name="twitter:..." tags, documents twitter:image:alt for accessible image descriptions, and says SVG is not supported for card images. Keeping the shared layout aligned with that markup makes the home page social metadata easier for card crawlers and validators to consume.

Reference: https://developer.x.com/cards/markup

Validation

• magick public/og-image.svg public/og-image.png
• file public/og-image.png and identify public/og-image.png confirmed a 1200x630 PNG
• pnpm build
• Confirmed built dist/index.html contains meta name="twitter:card", twitter:title, twitter:description, twitter:image, twitter:image:alt, twitter:creator, and twitter:site
• Confirmed built dist/index.html contains og:image, og:image:alt, and points image metadata to https://firstcontributions.github.io/og-image.png
• Confirmed built dist/og-image.png exists as a 1200x630 PNG
• Confirmed built home <title>, og:title, and twitter:title are 62 characters
• Confirmed built dist/index.html no longer contains meta property="twitter:*" tags for the home page
• git diff --check

Contributes to #348.

[Sean-Kenneth-Doherty]

Withdrawing this to keep the contribution queue focused on the highest-signal fixes. I opened too many small slices here, and this one is less important than the concrete broken-link, security, workflow, rendering, and accessibility fixes that remain open.