fix: Custom step navigation bugs - go-back, descendants, redundant checkbox

- Show previously-created custom steps as clickable options on decision
  nodes so they remain accessible after going back
- Fix breadcrumb to show custom step titles instead of raw UUIDs
- Fix ContinuationModal to show grandchildren (two levels deep) instead
  of immediate children that duplicate option labels
- Remove redundant "Save to Library" checkbox from StepForm since
  PostStepActionModal now handles that decision

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/step-library/CustomStepModal.tsx

@@ -36,9 +36,7 @@ export function CustomStepModal({ isOpen, onClose, onInsertStep }: CustomStepMod
 
   if (!isOpen) return null
 
-  const handleFormSubmit = async (data: StepCreate, _saveToLibrary: boolean) => {
-    // Note: saveToLibrary preference is no longer used here - the PostStepActionModal
-    // handles the decision of whether to save to library, use now, or both
+  const handleFormSubmit = async (data: StepCreate) => {
     setIsSubmitting(true)
     setError(null)
 

frontend/src/components/step-library/StepForm.tsx

@@ -5,7 +5,7 @@ import { stepCategoriesApi } from '@/api'
 import type { StepCreate, StepCategory, StepCommand } from '@/types/step'
 
 interface StepFormProps {
-  onSubmit: (data: StepCreate, saveToLibrary: boolean) => void
+  onSubmit: (data: StepCreate) => void
   onCancel: () => void
   initialData?: Partial<StepCreate>
 }
@@ -31,8 +31,6 @@ export function StepForm({ onSubmit, onCancel, initialData }: StepFormProps) {
   const [visibility, setVisibility] = useState<'private' | 'team' | 'public'>(
     initialData?.visibility || 'private'
   )
-  const [saveToLibrary, setSaveToLibrary] = useState(true)
-
   // Categories
   const [categories, setCategories] = useState<StepCategory[]>([])
 
@@ -131,7 +129,7 @@ export function StepForm({ onSubmit, onCancel, initialData }: StepFormProps) {
       tags: tags.length > 0 ? tags : undefined
     }
 
-    onSubmit(data, saveToLibrary)
+    onSubmit(data)
   }
 
   return (
@@ -367,20 +365,6 @@ export function StepForm({ onSubmit, onCancel, initialData }: StepFormProps) {
         </select>
       </div>
 
-      {/* Save to Library Checkbox */}
-      <div className="flex items-center gap-2">
-        <input
-          type="checkbox"
-          id="saveToLibrary"
-          checked={saveToLibrary}
-          onChange={(e) => setSaveToLibrary(e.target.checked)}
-          className="h-4 w-4 rounded border-input"
-        />
-        <label htmlFor="saveToLibrary" className="text-sm">
-          Save to My Step Library for reuse
-        </label>
-      </div>
-
       {/* Actions */}
       <div className="flex gap-2 pt-4">
         <button