feat(vegetation): wire arbre/sapin/buisson into LOD system

Register the three new vegetation LOD models in MAP_LOD_MODEL_PATHS and
extend VegetationSystem with per-chunk distance-based LOD selection
(mirroring MapInstancingSystem). Chunk model paths are re-evaluated on
the existing CHUNK_CONFIG.updateInterval cadence and Suspense keys
include the resolved path so a swap unmounts the previous instanced mesh
cleanly.

src/data/world/mapLodConfig.ts

@@ -14,6 +14,9 @@ export const MAP_LOD_MODEL_PATHS = {
   maison1: "/models/maison1-LOD/model.gltf",
   panneauaffichage: "/models/panneauaffichage-LOD/model.gltf",
   talkie: "/models/talkie-LOD/model.gltf",
+  arbre: "/models/arbre-LOD/model.glb",
+  buisson: "/models/buisson-LOD/model.glb",
+  sapin: "/models/sapin-LOD/model.glb",
 } as const satisfies Record<string, string>;
 
 export function getMapLodModelPath(modelName: string): string | null {