fix: add image alt text to logo (#331)

# Description

To improve accessibility. 

This PR needs no review.

## Checklist

- [X] Ran `just run-all`

Author: signekb

index.qmd

@@ -4,6 +4,7 @@ toc: false
 sidebar: false
 page-layout: custom
 image: _extensions/seedcase-project/seedcase-theme/logos/seedcase-logo.svg
+image-alt: Seedcase logo.
 about:
   id: hero-heading
   template: solana