feat(spatial): 空间查询和索引系统 (#324)

* feat(spatial): 添加空间查询包

- ISpatialQuery: 空间查询接口
  - findInRadius, findInRect, findNearest, findKNearest
  - raycast, raycastFirst
  - IBounds, IRaycastHit, SpatialFilter 类型

- ISpatialIndex: 空间索引接口
  - insert, remove, update, clear, getAll

- GridSpatialIndex: 网格空间索引实现
  - 基于均匀网格的空间划分
  - 支持所有 ISpatialQuery 操作

- 工具函数
  - createBounds, isPointInBounds, boundsIntersect
  - distanceSquared, distance

* feat(spatial): 添加空间查询蓝图节点

- 添加 FindInRadius/FindInRect/FindNearest/FindKNearest 节点
- 添加 Raycast/RaycastFirst 射线检测节点
- 每个节点包含模板和执行器
- 使用 menuPath: ['Spatial', ...] 组织节点菜单

packages/spatial/module.json

@@ -0,0 +1,23 @@
+{
+    "id": "spatial",
+    "name": "@esengine/spatial",
+    "globalKey": "spatial",
+    "displayName": "Spatial Query",
+    "description": "空间查询和索引系统 | Spatial query and indexing system",
+    "version": "1.0.0",
+    "category": "Core",
+    "icon": "Grid",
+    "tags": ["spatial", "query", "quadtree", "grid"],
+    "isCore": false,
+    "defaultEnabled": true,
+    "isEngineModule": true,
+    "canContainContent": false,
+    "platforms": ["web", "desktop", "server"],
+    "dependencies": ["core", "math"],
+    "exports": {
+        "components": [],
+        "systems": ["SpatialIndexSystem"]
+    },
+    "outputPath": "dist/index.js",
+    "pluginExport": "SpatialPlugin"
+}