Swapped in the new Open Graph image (2400x1260), keeping the OG-hallmark.png
filename so the meta tags, the README banner, and the deployed URL all stay
valid; updated the height meta to match.
Refreshed the "Different briefs, different shapes" gallery to the worked
examples we actually ship now: the four new themes (Bubble, Distil, Cold Snap,
Cinder), the Custom and newly generated pages (Mend Assembly, Hollowback Apiary,
Off-Register, Press Quaternary), and four originals (Tally, Wayfare, NAJM,
Hyperlane). Dropped the retired examples, reworded the intro, and added eight
new hero shots.
Youssef
