Wire shelf + spawn placement polish: SFX, cursor, sidebar, selection

User-visible follow-ups after first running the Phase 2 spike.

Spawn tool now matches legacy UX:
- CursorSphere from @pascal-app/editor for the placement indicator
  (ring + line + tool-icon tooltip) — was a plain sphere mesh.
- Emits sfx:structure-build on commit + setTool(null) + setMode
  ('select') to exit build mode, matching legacy spawn-tool.

Shelf tool placement:
- Emits sfx:structure-build on commit.
- Cursor preview now shows top board + brackets (was just the top),
  matching what gets placed.

Shelf selectable from the 3D canvas:
- ShelfEvent type added to @pascal-app/core/events/bus.
- 'shelf' added to NodeConfig in useNodeEvents.
- ShelfRenderer wires `useNodeEvents(node, 'shelf')` handlers onto
  every mesh. Clicks/hovers now bubble through the editor's selection
  manager and update useViewer.selection.

Shelf appears in the sidebar:
- ShelfTreeNode component (mirrors spawn-tree-node's shape +
  selection/hover/rename wiring; lucide Layers icon).
- TreeNode dispatcher adds a `case 'shelf':` arm.

Framework changes:
- @pascal-app/editor exports CursorSphere alongside triggerSFX.
- @pascal-app/nodes now declares @pascal-app/editor as peer/dev dep.

Pre-existing typecheck errors in @pascal-app/editor (ceiling-tree-node,
fence-tree-node, slab-tree-node, scene.ts) are unchanged — present on
main and not introduced by this commit.

630 tests still pass.

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

packages/viewer/src/hooks/use-node-events.ts

@@ -21,6 +21,8 @@ import {
   type RoofNode,
   type RoofSegmentEvent,
   type RoofSegmentNode,
+  type ShelfEvent,
+  type ShelfNode,
   type SiteEvent,
   type SiteNode,
   type SlabEvent,
@@ -49,6 +51,7 @@ type NodeConfig = {
   building: { node: BuildingNode; event: BuildingEvent }
   level: { node: LevelNode; event: LevelEvent }
   zone: { node: ZoneNode; event: ZoneEvent }
+  shelf: { node: ShelfNode; event: ShelfEvent }
   slab: { node: SlabNode; event: SlabEvent }
   spawn: { node: SpawnNode; event: SpawnEvent }
   ceiling: { node: CeilingNode; event: CeilingEvent }