Executor now applies rotation, flip, resize, watermark, format
conversion, compression, renaming, and metadata handling. Previously
only resize, convert, and compress were active.
- Rotation: CW90/180/270 via image crate methods
- Flip: horizontal/vertical via image crate methods
- Watermark: text (imageproc + ab_glyph) and image overlay with
alpha blending, positioned via WatermarkPosition enum
- Rename: apply_simple or template-based renaming with counter
- Metadata: re-encoding strips EXIF; KeepAll copies back via little_exif
The executor now uses rayon's thread pool for parallel processing when
thread_count > 1. Progress updates are sent via mpsc channel from worker
threads. Falls back to sequential processing for thread_count = 1.
The PipelineExecutor now stores thread_count and pause_on_error
fields. When pause_on_error is enabled, the executor sets the
pause flag on failures so the user can review errors. The GUI
reads these settings from AppConfig before starting processing.
