Phase 5 Stage E: full kind migration into packages/nodes

Wholesale move of every remaining kind into its own subdirectory under
`packages/nodes/src/`, finishing the registry-driven migration. Each
kind now ships its definition, schema (re-exported from core), and any
of `geometry` / `renderer` / `system` / `floorplan` / `tool` /
`move-tool` / `panel` / `floorplan-move` / `floorplan-affordances` /
`parametrics` / `preview` it needs — no per-kind code remains under
`packages/editor/src/components/tools/` or
`packages/viewer/src/components/renderers/`.

Deleted (replaced by registry-driven equivalents):
- `tools/{ceiling,column,door,fence,item,slab,spawn,wall,window}/...`
  (boundary editors, hole editors, placement tools, move tools,
  endpoint movers, curve tools, helpers, math libs)
- `ui/helpers/{ceiling,slab,wall}-helper.tsx`
- `ui/panels/{column,door,elevator,item,roof,roof-segment,spawn,
  stair,stair-segment,wall,window}-panel.tsx`
- `viewer/src/components/renderers/{building,ceiling,column,door,
  elevator,fence,guide,item,level,roof,roof-segment,scan,site,slab,
  spawn,stair,stair-segment,wall,window,zone}-renderer.tsx`
- `viewer/src/components/viewer/legacy-system.tsx`

Added under `packages/nodes/src/`:
- `building/`, `column/`, `elevator/`, `guide/`, `level/`, `roof/`,
  `roof-segment/`, `scan/`, `shared/`, `site/`, `stair/`,
  `stair-segment/` packages with definition + schema + renderer / system
  / floorplan / panel as appropriate.
- New `floorplan-move.ts` for every kind that supports 2D moves
  (ceiling, door, item, shelf, slab, window) — single registry-driven
  dispatch path via `def.floorplanMoveTarget`.
- New `floorplan-affordances.ts` for kinds with polygon / endpoint
  drags (ceiling, fence, slab, wall) — using the shared
  `polygon-vertex-affordance` factories.
- New per-kind `panel.tsx` for kinds with custom inspector content
  (door, item, shelf, spawn, wall, window).
- New per-kind `tool.tsx` for placement (door, item, shelf, window).
- New per-kind `move-tool.tsx` for kinds with custom 3D move flows
  (door, item, slab, window).

Coordinator + manager updates in `packages/editor/`:
- `tool-manager.tsx` resolves tools from the registry only — no
  hardcoded type→component map.
- `panel-manager.tsx` resolves inspector panels the same way.
- `placement-{coordinator,strategies,types}.ts` extended with
  shelf-surface placement.
- `selection-manager.tsx` adds the registry-selectable fallback.
- `floorplan-panel.tsx`, `floorplan-background-placement.ts`,
  `floorplan-render-context.tsx` updated for the registry layer's new
  contract (props, affordance dispatch, render context).

Viewer updates:
- `viewer/index.tsx` drops legacy renderer mounts.
- `node-renderer.tsx` resolves by registry only.
- `scene-bvh.tsx`, `use-node-events.ts`, `level-system.tsx`,
  `wall-cutout.tsx`, `zone-system.tsx`, `materials.ts` adjusted for
  the registry-only world.

Sidebar tree nodes for ceiling / fence / slab / shelf / tree-node
updated to read from the registered nodes instead of the deleted
legacy renderer trees.

Wiki: new `plugin-authoring.md` page, README index updated.

Tests in `packages/nodes/src/index.test.ts` validate every registered
kind has the required shape.

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

packages/nodes/src/roof-segment/floorplan.ts

@@ -0,0 +1,106 @@
+import type {
+  FloorplanGeometry,
+  FloorplanPoint,
+  GeometryContext,
+  RoofNode,
+  RoofSegmentNode,
+} from '@pascal-app/core'
+
+/**
+ * Stage C floor-plan builder for roof segment. Renders the segment's
+ * footprint as a rotated rectangle in world coords (parent roof's
+ * position + rotation composed with the segment's own).
+ *
+ * Inlined from `getRoofSegmentPolygon` / `getRoofSegmentCenter` in
+ * `floorplan-panel.tsx`. Ridge line not yet rendered — adds a follow-up
+ * for full visual parity.
+ */
+export function buildRoofSegmentFloorplan(
+  node: RoofSegmentNode,
+  ctx: GeometryContext,
+): FloorplanGeometry | null {
+  const roof = ctx.parent as RoofNode | null
+  if (!roof || roof.type !== 'roof') return null
+
+  // Segment center in world coords: parent roof's transform applied to
+  // the segment's local position offset.
+  const cosRoof = Math.cos(roof.rotation)
+  const sinRoof = Math.sin(roof.rotation)
+  const localX = node.position[0]
+  const localZ = node.position[2]
+  const cx = roof.position[0] + localX * cosRoof - localZ * sinRoof
+  const cz = roof.position[2] + localX * sinRoof + localZ * cosRoof
+
+  const rotation = roof.rotation + node.rotation
+  const cos = Math.cos(rotation)
+  const sin = Math.sin(rotation)
+  const halfWidth = node.width / 2
+  const halfDepth = node.depth / 2
+
+  const corners: Array<[number, number]> = [
+    [-halfWidth, -halfDepth],
+    [halfWidth, -halfDepth],
+    [halfWidth, halfDepth],
+    [-halfWidth, halfDepth],
+  ]
+  const points: FloorplanPoint[] = corners.map(([x, y]) => [
+    cx + x * cos - y * sin,
+    cz + x * sin + y * cos,
+  ])
+
+  const view = ctx.viewState
+  const palette = view?.palette
+  const isSelected = view?.selected ?? false
+  const isHighlighted = view?.highlighted ?? false
+  const showSelectedChrome = isSelected || isHighlighted
+
+  const stroke =
+    showSelectedChrome && palette ? palette.selectedStroke : 'rgba(125, 211, 252, 0.82)'
+  const fill = showSelectedChrome ? '#fed7aa' : 'rgba(56, 189, 248, 0.16)'
+
+  const children: FloorplanGeometry[] = [
+    {
+      kind: 'polygon',
+      points,
+      fill,
+      stroke,
+      strokeWidth: showSelectedChrome ? 0.04 : 0.025,
+      strokeLinejoin: 'round',
+      opacity: 0.85,
+    },
+  ]
+
+  // Ridge line — only for pitched segments, not flat roofs.
+  if (node.roofType !== 'flat') {
+    const ridgeAxis =
+      node.roofType === 'gable' || node.roofType === 'gambrel'
+        ? 'x'
+        : node.roofType === 'dutch'
+          ? node.width >= node.depth
+            ? 'x'
+            : 'z'
+          : 'z'
+    const axisAngle = ridgeAxis === 'x' ? rotation : rotation + Math.PI / 2
+    const halfSpan = ridgeAxis === 'x' ? node.width / 2 : node.depth / 2
+    children.push({
+      kind: 'line',
+      x1: cx - halfSpan * Math.cos(axisAngle),
+      y1: cz - halfSpan * Math.sin(axisAngle),
+      x2: cx + halfSpan * Math.cos(axisAngle),
+      y2: cz + halfSpan * Math.sin(axisAngle),
+      stroke: showSelectedChrome ? '#eff6ff' : 'rgba(186, 230, 253, 0.84)',
+      strokeWidth: 1.4,
+      strokeLinecap: 'round',
+      vectorEffect: 'non-scaling-stroke',
+    })
+  }
+
+  if (isSelected) {
+    children.push({
+      kind: 'move-handle',
+      point: [cx, cz],
+    })
+  }
+
+  return { kind: 'group', children }
+}