docs: redesign social-preview card to the bold blueprint look

Higher-contrast white-ground design per the approved reference: heavier
wordmark, filled stage icons in thick rounded boxes, bold black data-flow
arrows with vermilion key nodes, padlock on the BRAND-LOCK bar, bold caps
REVISE LOOP, pill-bordered spec/date blocks. Same v0.2.0 content
(critique.json, the revise loop, brand-lock-extractor).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Yuri Strohm