- add __post_init__ to GradingParams to coerce Gradio int returns to float
- apply CLAHE to L channel in Lab space instead of per-RGB channel
- fix sharpness scaling (kornia factor 1.0=no change, map 0-based slider)
- increase shadows/midtones/highlights gamma strength 2x for visible effect
- reduce CLAHE clip slider range to 0-5 with finer 0.25 step