Fix logo transparency: preserve owl body while clearing letter counters

Use region-based approach: flood-fill from corners for outer background,
then apply transparency only to the text region (below the owl) to clear
letter counter interiors (P, A, e, a) without affecting the owl's
white/cream body areas.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: laughingman7743