Adds a simplified graphical node editor as the workflow editor's default
view: a modern vertical auto-laid-out React Flow canvas with insert-on-edge
"+" affordances and a searchable, categorized add-step dialog (node kinds +
fragments + step templates). A segmented Simple/Advanced/List switch
(persisted in localStorage) keeps the full advanced canvas untouched and
retains the old compact row editor as the List fallback. Mobile's graph tab
gains the touch-friendly simplified canvas with the row list as fallback.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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