Color grading mutated pp.image but never wrote to pp.info, so the
chosen brightness/contrast/gamma/LUT/etc. were invisible in the
saved file's postprocessing/extras chunks and in the live Output
panel — unlike every other postprocessor (Upscale, Rembg, NudeNet,
PixelArt) which all stamp their settings.
Stamp every non-default GradingParams field as 'Grading <name>' so
the trail is consistent with the rest of the Process tab. LUT file
is recorded by basename rather than full path to keep the metadata
string compact.