The canvas and list add-node menus both listed all 10 node types in
one flat dropdown. As the type list grows — especially for forks
adding their own node types (see #312) — a flat list gets hard to
scan. Bucket the types into Messaging / Logic & data / Flow control,
driven by a new `category` field on NODE_META so a new type can't go
uncategorized, and a `groupNodeTypesByCategory` helper shared by both
menus so they stay in lockstep.
No triggers/events category: in wacrm a flow is triggered by
flow-level config (trigger_type), not a canvas node, so `start` lives
under Flow control.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
