[SEO] Create social preview image (og:image / twitter:image)

[wi287g]

Every link share on social media shows no preview image until this is created.

Spec

• Size: 1200 × 630 px PNG (og:image standard)
• File path: docs/img/social-preview.png
• Already referenced in index.html

Suggested content
Screenshot of the dashboard map with county colors visible + title text overlay:
"Wisconsin 287(g) & ICE Detainer Dashboard — wi287g.github.io/dashboard"

Also needed for docs/img/

• favicon.png — 32×32 px PNG (export from favicon.svg)
• apple-touch-icon.png — 180×180 px (iOS home screen)

Tooling
Figma (free), GIMP, Canva, or screenshot + annotate in any image editor.

Once created, also upload to: repo → Settings → Social preview (separate from og:image — controls what GitHub shows when the repo link is shared).