Add src/main/ImageOperations.js (convert/resize/compress/rotate via
sharp), modeled on PDFOperations.js's executeOperation dispatcher.
Wire ipcMain.handle('process-image-operation', ...) in main.js using
sanitizeErrorMessage() on error paths, and replace the 5 stale/unused
image-* channel names in preload.js's ALLOWED_SEND_CHANNELS with
process-image-operation + select-image-folder (mirroring
select-pdf-folder for a later batch-UI task).
Amit Haridas
