Show numeric sub-variation edge values as bare numbers

Numeric dependsOn values (merge-type variations) are RFC edge values,
not ATTR names. Display them as the number, not as "ATTR: N" or
"subvariation N".

static/components/PaneCP.js

@@ -15,12 +15,13 @@ function shortView(node) {
             };
         case 'instrument':
             return { typeTag: 'instrument', label: node.name, meta: [] };
-        case 'variation':
-            return {
-                typeTag: 'variation',
-                label: node.dependsOn ? `ATTR: ${node.dependsOn}` : '(root variation)',
-                meta: [],
-            };
+        case 'variation': {
+            const dep = node.dependsOn;
+            const label = dep == null ? '(root variation)'
+                : isNaN(Number(dep)) ? `ATTR: ${dep}`
+                : String(dep);
+            return { typeTag: 'variation', label, meta: [] };
+        }
         case 'label_spec':
             return { typeTag: 'label', label: node.label ?? '(no label)', meta: [] };
         case 'bar':