Feat/stairs fence update (#226)

* feat: railing on the straight stairs and new fence

* feat: added spiral and curved stairs with bug fix for fence

* feat:fence are linked to each other ... so moving one move the other sharing the same coordinate

* fix: update stair railing logic to include front-side attachments for terminal landings

* Integrate fence rendering into the fence system

* fix: pass nodeId instead of undefined node to WallTreeNode and FenceTreeNode

TreeNode was passing `node` (undefined variable) instead of `nodeId` to
WallTreeNode and FenceTreeNode, causing a runtime ReferenceError.
Updated FenceTreeNode to accept nodeId and look up the node from the
scene store internally, consistent with all other tree node components.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: update fence icon with new isometric design

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Aymeric Rabot <aymeric@pascal.app>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

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

@@ -7,6 +7,8 @@ import {
   type DoorNode,
   type EventSuffix,
   emitter,
+  type FenceEvent,
+  type FenceNode,
   type ItemEvent,
   type ItemNode,
   type LevelEvent,
@@ -37,6 +39,7 @@ type NodeConfig = {
   site: { node: SiteNode; event: SiteEvent }
   item: { node: ItemNode; event: ItemEvent }
   wall: { node: WallNode; event: WallEvent }
+  fence: { node: FenceNode; event: FenceEvent }
   building: { node: BuildingNode; event: BuildingEvent }
   level: { node: LevelNode; event: LevelEvent }
   zone: { node: ZoneNode; event: ZoneEvent }