Downscales an image to fit within a maximum dimension (default 1600px on the longer side, never enlarges -- matching GO AI's browser compressor tool) and re-encodes it as JPEG, WebP or AVIF at a given quality (1-100 scale, default 75). Input is base64-encoded image bytes (any format sharp/libvips can decode: JPEG, PNG, WebP, AVIF, GIF, TIFF, ...), not a file path or URL, capped at this server's input size limit. Returns the compressed image bytes plus a stats object: original and compressed dimensions and byte sizes, and the percent size change (positive = smaller, negative = the re-encode came out bigger, which happens when compressing an already-small, already-compressed image). Re-encoding always strips EXIF/ICC metadata, exactly like the source tool.