fix(hatch): radial gradient stops run outside-in

SPHERICAL/HEMISPHERICAL gradients painted colour 1 at the centre;
AutoCAD's convention is colour 1 at the rim and colour 2 at the centre
(the INV variants swap them back). Both the native and the WebGL2
shader now mix the radial branch outside-in; linear/cylinder/curved
are untouched.

Co-Authored-By: Claude Fable 5 <[email protected]>

src/shaders/hatch.wgsl

@@ -313,7 +313,10 @@ fn check_family(
         if (inst.grad_kind & 16u) != 0u {
             t = 1.0 - t;
         }
-        return mix(inst.color, inst.color2, t);
+        // Radial stops run OUTSIDE-IN: colour 1 at the rim, colour 2 at the
+        // centre (AutoCAD's SPHERICAL/HEMISPHERICAL convention; the INV bit
+        // above swaps them back).
+        return mix(inst.color2, inst.color, t);
     }
 
     // 3. Pattern LOD: when the densest family's spacing projects below

src/shaders/hatch_web.wgsl

@@ -268,7 +268,8 @@ fn check_family(
         if ginv {
             t = 1.0 - t;
         }
-        return mix(h.color, h.color2, t);
+        // Radial stops run outside-in (colour 2 at the centre) — see hatch.wgsl.
+        return mix(h.color2, h.color, t);
     }
 
     // Pattern LOD: when the densest family projects below 2 px, lines blur into