docs(styling): new thumbnail capturing the full styling story

Replace the dark single-facet label overlay with one coherent scene:
crimson/gold double-outlined translucent polygons (fill opacity + the
new double outline) over white segmentation contours on the blobs image
— shapes styling and label boundaries in one frame.

Claude-Session: https://claude.ai/code/session_01U9J5GSXR4XGjPMaQQR5iSj

Author: timtreis