- Add EncoderOptions struct with progressive_jpeg and avif_speed fields
- Pass encoder options through ProcessingJob to PipelineExecutor
- mozjpeg set_progressive_mode() called when progressive JPEG enabled
- AVIF encoder speed now configurable (was hardcoded to 6)
- run_processing uses CompressConfig::Custom when user overrides preset defaults
- Executor properly handles AVIF quality and PNG level in Custom mode