feat(debug): add player model and octree visualization toggles

- Show Player Model: render the main character GLTF in camera-local
  space so it stays visible at any pitch.
- Show Octree: overlay the collision octree as colored line segments,
  one wireframe per spatial cell, colored by depth.
- Octree Max Depth: cap recursion to keep the scene readable.

src/managers/stores/useDebugVisualsStore.ts

@@ -0,0 +1,19 @@
+import { create } from "zustand";
+
+interface DebugVisualsStore {
+  showPlayerModel: boolean;
+  setShowPlayerModel: (value: boolean) => void;
+  showOctree: boolean;
+  setShowOctree: (value: boolean) => void;
+  octreeMaxDepth: number;
+  setOctreeMaxDepth: (value: number) => void;
+}
+
+export const useDebugVisualsStore = create<DebugVisualsStore>((set) => ({
+  showPlayerModel: false,
+  setShowPlayerModel: (showPlayerModel) => set({ showPlayerModel }),
+  showOctree: false,
+  setShowOctree: (showOctree) => set({ showOctree }),
+  octreeMaxDepth: 6,
+  setOctreeMaxDepth: (octreeMaxDepth) => set({ octreeMaxDepth }),
+}));