docs: add verified YouTube history deletion trace (score 0.75, 3/4 milestones)

Customer's exact task UUID (44ee5668). Claude planner + UI-Venus grounder
on WAA VM with all fixes applied (#147, #148). 6 steps: opened Chrome
history → selected YouTube entries → clicked Delete → confirmed dialog →
verified history cleared.

Tested: Docker build verified, container booted, experiment completed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abrichr