iPhone photos with depth maps or gain maps have too many auxiliary
image references for libheif 1.17, causing pillow-heif to throw
"Too many auxiliary image references". process_heic_image() now
falls back to ffmpeg when pillow-heif fails — ffmpeg's own HEIC
decoder handles these files without issue. Fixes 27/35 HEIC photos
that were stuck in failed state.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>