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/core/src/events/bus.ts

@@ -13,6 +13,7 @@ import type {
   LevelNode,
   RoofNode,
   RoofSegmentNode,
+  ShelfNode,
   SiteNode,
   SlabNode,
   SpawnNode,
@@ -57,6 +58,7 @@ export type SiteEvent = NodeEvent<SiteNode>
 export type BuildingEvent = NodeEvent<BuildingNode>
 export type LevelEvent = NodeEvent<LevelNode>
 export type ZoneEvent = NodeEvent<ZoneNode>
+export type ShelfEvent = NodeEvent<ShelfNode>
 export type SlabEvent = NodeEvent<SlabNode>
 export type SpawnEvent = NodeEvent<SpawnNode>
 export type CeilingEvent = NodeEvent<CeilingNode>
@@ -189,6 +191,7 @@ type EditorEvents = GridEvents &
   NodeEvents<'level', LevelEvent> &
   NodeEvents<'zone', ZoneEvent> &
   NodeEvents<'slab', SlabEvent> &
+  NodeEvents<'shelf', ShelfEvent> &
   NodeEvents<'spawn', SpawnEvent> &
   NodeEvents<'ceiling', CeilingEvent> &
   NodeEvents<'column', ColumnEvent> &

packages/core/src/index.ts

@@ -14,6 +14,7 @@ export type {
   NodeEvent,
   RoofEvent,
   RoofSegmentEvent,
+  ShelfEvent,
   SiteEvent,
   SlabEvent,
   SpawnEvent,