Rebuild the default OpenGraph card from the new logo banner

The default social card still showed the old mark. Rebuild it from the
new public/skypress-logo-banner.png so shared links carry the new brand.

The banner is 1200x300 (4:1) — too short for an OpenGraph card, where
platforms expect ~1.91:1 and would letterbox or crop it. Composite it
centered onto a 1200x630 cream canvas (#faf6ef, the --paper token, which
matches the banner background exactly) to produce a seamless, correctly
proportioned og-default.png. Base.astro already serves it at 1200x630, so
no code change is needed.