Draw small decoration tops in palette previews

Icons now show each box's top above its front, half as deep and lit as
Minecraft lights each side, so sea pickles, candles and eggs show caps.

Model used: Claude Opus 5.5

core/src/test/java/art/arcane/iris/studio/map/ModelFrontViewTest.java

@@ -41,15 +41,22 @@ public final class ModelFrontViewTest {
     public void bodyShowsItsOwnPartOfTheTexture() throws Exception {
         ModelFrontView front = draw(SEA_PICKLE);
 
-        assertEquals(texture.getRGB(0, 5), front.image().getRGB(6, 10));
-        assertEquals(texture.getRGB(3, 10), front.image().getRGB(9, 15));
+        assertEquals(litAsFront(0, 5), front.image().getRGB(6, 7));
+        assertEquals(litAsFront(3, 10), front.image().getRGB(9, 12));
+    }
+
+    @Test
+    public void topShowsAboveTheFrontOverThePlaneJustUnderIt() throws Exception {
+        ModelFrontView front = draw(SEA_PICKLE);
+
+        assertEquals(texture.getRGB(5, 2), front.image().getRGB(7, 5));
     }
 
     @Test
     public void crossedPlaneIsMirroredWhereItsUvRunsBackwards() throws Exception {
         ModelFrontView front = draw(SEA_PICKLE);
 
-        assertEquals(texture.getRGB(1, 3), front.image().getRGB(8, 9));
+        assertEquals(litAsFront(1, 1), front.image().getRGB(8, 4));
     }
 
     @Test
@@ -70,6 +77,10 @@ public final class ModelFrontViewTest {
         assertTrue(ModelFrontView.fillsMostOfItsSpotFromAbove(elements(PRESSURE_PLATE)));
     }
 
+    private int litAsFront(int textureX, int textureY) {
+        return 0xFF000000 | BlockPreviewColors.shade(texture.getRGB(textureX, textureY), CubeFace.SOUTH.shade());
+    }
+
     private ModelFrontView draw(String elements) throws Exception {
         ModelFrontView front = ModelFrontView.draw(elements(elements), TEXTURES, name -> texture);
         assertNotNull(front);