fix(heal): eliminate boundary seams by windowing inpaint clusters to 1:1 scale and smoothing feather transition

docker/frontend/shared/utils/heal.ts

@@ -25,9 +25,9 @@ import type { HealSpot } from '../types';
 export const HEAL_DEFAULT_R = 0.012;
 
 // How much of a spot is painted at full strength, as a fraction of its radius:
-// out to 95% the mask is solid to completely eliminate defects without leaving
-// residual dirt/shadows, and the last 5% is a smooth Hermite fade to blend into the photo.
-export const HEAL_FEATHER = 0.95;
+// out to 75% the mask is solid to completely eliminate defects, and the outer 25%
+// is a smooth Hermite fade (smoothstep) to blend invisibly into the surrounding photo.
+export const HEAL_FEATHER = 0.75;
 
 // The finest of the fill's blurs, as a multiple of the widest brush in the
 // stroke. The light of the rim has to reach the middle of the hole, so the