blog: add cover image to "Hyprnote is now Char" post

[devin-ai-integration]

blog: add cover image to "Hyprnote is now Char" post

Summary

Adds a coverImage frontmatter field to the "Hyprnote is now Char" blog post, using the image proxy path /api/images/blog/announcement.jpg (consistent with other blog posts in the repo). This post was previously missing a cover image.

The proxy route (/api/images/$) resolves to the upstream Supabase storage URL https://auth.hyprnote.com/storage/v1/object/public/public_images/blog/announcement.jpg.

Review & Testing Checklist for Human

• Verify the image loads at /api/images/blog/announcement.jpg on the deployed preview (i.e. the file exists in Supabase storage)
• After deploy, check that the cover image renders on char.com/blog/hyprnote-is-now-char/ and on the blog listing page
• Verify OG/social meta tags include the cover image URL correctly

Notes

Requested by: @ComputelessComputer
Link to Devin run

[devin-ai-integration]

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