fix(og-image): match sim.ai OG image colors to live landing tokens (#5592)

The wordmark ink and background were slightly off from the actual
site: #1a1a1a on #f8f8f8 in the static OG asset vs var(--text-body)
(#3b3b3b) on var(--bg) (#fefefe) as rendered on the live landing page.
Recolored the same wordmark artwork in place to match exactly - alpha
reconstructed from the existing two-color image and recomposited onto
the new colors, so the glyph geometry/anti-aliasing is unchanged.

Author: waleedlatif1