Handle HTML fallbacks for node help and skip blueprint docs (#7021)

explicitly prevents subgraphs from making an api call since they don't
have docs, this was previously reliant on a non-ok resolution

also doesn't try returning anything that has contenttype of text/html to
prevent the markdown renderer from crashing

## Summary
- short-circuit blueprint/subgraph nodes in help: skip doc fetch and
return the node description, avoiding SPA fallback responses
- guard node help fetch against HTML/SPA fallbacks using content-type
checks; treat them as missing and trigger the existing description
fallback
- keep base URL logic unchanged for non-blueprint nodes

## Testing
- pnpm typecheck
- pnpm lint:fix
- pnpm test:unit

src/workbench/utils/nodeHelpUtil.ts

@@ -15,6 +15,9 @@ export function extractCustomNodeName(
 
 export function getNodeHelpBaseUrl(node: ComfyNodeDefImpl): string {
   const nodeSource = getNodeSource(node.python_module)
+  if (nodeSource.type === NodeSourceType.Blueprint) {
+    return ''
+  }
   if (nodeSource.type === NodeSourceType.CustomNodes) {
     const customNodeName = extractCustomNodeName(node.python_module)
     if (customNodeName) {