fix: add optional chaining to nodeDef access in NodeTooltip (#5663)

## Summary

Extension of https://github.com/Comfy-Org/ComfyUI_frontend/pull/5659:
Added optional chaining to NodeTooltip component to prevent TypeError
when `nodeDef` is undefined for unknown node types.

## Changes

- **What**: Added [optional chaining
operator](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining)
(`?.`) to safely access `nodeDef` properties in NodeTooltip component

## Review Focus

Error handling for node types not found in nodeDefStore and tooltip
display behavior for unrecognized nodes.

Fixes CLOUD-FRONTEND-STAGING-3N

Co-authored-by: Claude <noreply@anthropic.com>

src/components/graph/NodeTooltip.vue

@@ -83,7 +83,7 @@ const onIdle = () => {
     const inputName = node.inputs[inputSlot].name
     const translatedTooltip = st(
       `nodeDefs.${normalizeI18nKey(node.type ?? '')}.inputs.${normalizeI18nKey(inputName)}.tooltip`,
-      nodeDef.inputs[inputName]?.tooltip ?? ''
+      nodeDef?.inputs[inputName]?.tooltip ?? ''
     )
     return showTooltip(translatedTooltip)
   }
@@ -97,7 +97,7 @@ const onIdle = () => {
   if (outputSlot !== -1) {
     const translatedTooltip = st(
       `nodeDefs.${normalizeI18nKey(node.type ?? '')}.outputs.${outputSlot}.tooltip`,
-      nodeDef.outputs[outputSlot]?.tooltip ?? ''
+      nodeDef?.outputs[outputSlot]?.tooltip ?? ''
     )
     return showTooltip(translatedTooltip)
   }
@@ -107,7 +107,7 @@ const onIdle = () => {
   if (widget && !isDOMWidget(widget)) {
     const translatedTooltip = st(
       `nodeDefs.${normalizeI18nKey(node.type ?? '')}.inputs.${normalizeI18nKey(widget.name)}.tooltip`,
-      nodeDef.inputs[widget.name]?.tooltip ?? ''
+      nodeDef?.inputs[widget.name]?.tooltip ?? ''
     )
     // Widget tooltip can be set dynamically, current translation collection does not support this.
     return showTooltip(widget.tooltip ?? translatedTooltip)