Adds optional `presentation` field for tool palette metadata: sentence-
case label, optional description, icon (iconify reference, inline SVG,
or lazy React component), palette section override, sort order, and a
`hidden` flag for container kinds that exist but should not appear in
the palette.
Consumer arrives in Phase 4 (auto-derived palette buttons) — defining
the type now means Phase 2's `column` and `shelf` definitions ship with
the field already populated, no later round-trip.
Iconify is the encouraged form for built-ins and AI-authored nodes:
matches the @iconify-react setup the editor app already uses, and AI
emits a name string from a curated list (no asset upload step needed).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
