Decision 25 allows .webm/.ogg golden cases and decision 9 requires audio
fixtures to be committed; the ignore rule silently let a webm golden case
pass locally while failing on a clean clone (the fixture would never reach
git). Removes the `tests/fixtures/*.webm` line from .gitignore.
Refs #1
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
