Add a "Cyclic" gradient option that closes the ramp into a seamless loop (#4416)

* Add a Cyclic gradient attribute that wraps the stop list through the 1|0 boundary back to the first stop

* Show the wrap segment's midpoint diamond in the color picker spectrum strip when cyclic

* Keep the wrap midpoint diamond tracking the pointer by a wrapped strip width when dragged past the ends

* Give the Gradient tool's viewport overlay the same cyclic wrap midpoint diamond and drag behavior

* Correct the docs claiming the final stop's midpoint is always ignored now that cyclic uses it

* Move the gradient cyclic toggle onto the Ends row as a Link icon checkbox

* Update labels

* Register GradientHueDirection with the Data panel so its attribute column renders

* Reword wrap segment to wrapped interval and stray segment usages to interval

* Clean up comments

* Fix the color picker write-back losing default position elision and the blend path guessing the cyclic flag

node-graph/graph-craft/src/document/value.rs

@@ -1086,7 +1086,7 @@ mod gradient_shape_migration {
 		assert_eq!(ramp.gradient_space, GradientSpace::RgbGamma, "the pre-ramp flat form should carry the era's gamma");
 
 		let gradient = Gradient::from(ramp);
-		assert_eq!(gradient.positions(), vec![0., 0.25]);
+		assert_eq!(gradient.positions(false), vec![0., 0.25]);
 		assert!(gradient.has_midpoint_attribute(), "the flat form must parse faithfully");
 	}
 
@@ -1100,7 +1100,7 @@ mod gradient_shape_migration {
 		assert_eq!(ramp.gradient_space, GradientSpace::RgbGamma, "the pre-ramp tuple form should carry the era's gamma");
 
 		let gradient = Gradient::from(ramp);
-		assert_eq!(gradient.positions(), vec![0., 1.]);
+		assert_eq!(gradient.positions(false), vec![0., 1.]);
 		assert!(!gradient.has_position_attribute(), "even legacy tuple positions should elide");
 	}
 
@@ -1122,6 +1122,10 @@ mod gradient_shape_migration {
 		let TaggedValue::LegacyGradient(legacy) = load(json) else {
 			panic!("the ancient full struct should become a legacy gradient value")
 		};
-		assert_eq!(Gradient::from(legacy.stops).positions(), vec![0., 1.], "the nested tuple stops should parse through the field adapter");
+		assert_eq!(
+			Gradient::from(legacy.stops).positions(false),
+			vec![0., 1.],
+			"the nested tuple stops should parse through the field adapter"
+		);
 	}
 }