Phase 4 follow-on: registry-driven floor-plan rendering + shelf port

Adds the floor-plan side of the three-checkbox composition model
documented in wiki/architecture/node-definitions.md. Mirrors the 3D
side (def.geometry → <GeometrySystem> → <ParametricNodeRenderer>) but
emits SVG primitives instead of three.js Object3Ds, and runs inside
the floor-plan panel.

Type-side (packages/core/src/registry/types.ts):
 - New FloorplanGeometry tagged union covering path / polygon /
   polyline / rect / circle / line / group. FloorplanStyle props map
   straight to SVG attributes. Coordinates are level-local meters;
   rotations are radians (three.js convention).
 - New `def.floorplan?: (node, ctx) => FloorplanGeometry | null` field
   on NodeDefinition, independent of `geometry` and `renderer`. Re-
   exported via packages/core/src/registry/index.ts.

Runtime (packages/editor):
 - <FloorplanGeometryRenderer> walks the FloorplanGeometry tree and
   emits the matching React-SVG elements. Pure data → DOM; no per-kind
   logic.
 - <FloorplanRegistryLayer> reads the active levelId, walks the level
   subtree, looks up each node's def.floorplan, builds a
   GeometryContext, calls the builder, and renders the output via
   FloorplanGeometryRenderer.
 - Mounted in floorplan-panel.tsx just before <FloorplanMarqueeLayer>
   so registry-driven kinds layer above legacy inline content.

Shelf migration (proof port):
 - New nodes/src/shelf/floorplan.ts — buildShelfFloorplan(node) emits
   a group with the rotation/translation transform and a width × depth
   rectangle in the shelf's color. Brackets omitted (hidden under top
   board from above).
 - Wired to shelfDefinition.floorplan. Shelf now appears in the floor
   plan view for the first time (was missing from the legacy panel's
   inline switch).

Pattern proven; every future kind migrating in Phase 5 follows the
same shape: a pure (node, ctx) => FloorplanGeometry function. As kinds
register their floor-plan builders, the corresponding inline branches
in floorplan-panel.tsx become dead code and can be deleted in the
same PR.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/nodes/src/shelf/definition.ts

@@ -1,4 +1,5 @@
 import type { NodeDefinition } from '@pascal-app/core'
+import { buildShelfFloorplan } from './floorplan'
 import { buildShelfGeometry } from './geometry'
 import { shelfParametrics } from './parametrics'
 import { ShelfNode } from './schema'
@@ -43,14 +44,15 @@ export const shelfDefinition: NodeDefinition<typeof ShelfNode> = {
 
   parametrics: shelfParametrics,
 
-  // Three-checkbox composition: shelf needs only a pure geometry function.
-  // The framework's <ParametricNodeRenderer> mounts an empty group + wires
-  // events / registry / dirty-on-mount; the global <GeometrySystem> calls
-  // `buildShelfGeometry(node)` on every dirty mark and swaps the group's
-  // children. No `renderer.tsx`, no `system.tsx` — see
+  // Three-checkbox composition: shelf needs only pure builder functions.
+  // The framework's <ParametricNodeRenderer> + <GeometrySystem> handle 3D
+  // mount and rebuild on dirty; the <FloorplanRegistryLayer> calls
+  // buildShelfFloorplan for the 2D top-down view. No renderer.tsx, no
+  // system.tsx, no inline floor-plan SVG — see
   // `wiki/architecture/node-definitions.md`. Shelf is the reference port
-  // proving Phase 4's boilerplate collapse end-to-end.
+  // proving Phase 4's boilerplate collapse for both 3D and 2D.
   geometry: buildShelfGeometry,
+  floorplan: buildShelfFloorplan,
 
   preview: () => import('./preview'),
   tool: () => import('./tool'),