fix(docs): show '-' for blank inspector branch values, matching the canvas

inspectorFieldsFor passed raw branch.value into the lightbox branch fields, so an unset else route read blank in the inspector while DocsBlockNode (and the editor's getDisplayValue) render '-' on the canvas. Normalize the same way; drop the now-redundant placeholder.

Author: waleedlatif1

apps/docs/components/workflow-preview/workflow-preview.tsx

@@ -150,8 +150,8 @@ function inspectorFieldsFor(block: PreviewBlock) {
   const branchFields = (block.branches ?? []).map((branch) => ({
     label: branch.label,
     kind: 'code' as const,
-    value: branch.value,
-    placeholder: '—',
+    // Match the canvas + the editor's getDisplayValue: a blank value reads as '-'.
+    value: branch.value || '-',
   }))
   return [...rowFields, ...branchFields]
 }