fix(repair): drill explosion to natural group + apply mission rotation

- ExplodedModel.createParts now descends recursively through single
  mesh-bearing wrapper nodes (e.g. Scene > Moto > Eclatement) until
  reaching a node with multiple mesh-bearing children. Previously the
  first wrapper was used as root, so models with extra Empty/group
  parents fell back to flat leaf meshes lerping in local space.
- Add optional modelRotation field on RepairMissionConfig so fragmented
  + repairing models can match the world-space rotation of the source
  inspection model (parked Ebike).
- Ebike mission now uses EBIKE_WORLD_ROTATION_Y/EBIKE_WORLD_SCALE
  directly so the fragmented bike lines up with the parked bike.

src/components/three/gameplay/RepairGame.tsx

@@ -143,6 +143,7 @@ export function RepairGame({
         {step === "fragmented" ? (
           <ExplodableModel
             modelPath={config.modelPath}
+            rotation={config.modelRotation ?? [0, 0, 0]}
             scale={config.modelScale ?? 1}
             split
           />
@@ -160,6 +161,7 @@ export function RepairGame({
           <>
             <ExplodableModel
               modelPath={config.modelPath}
+              rotation={config.modelRotation ?? [0, 0, 0]}
               scale={config.modelScale ?? 1}
               split
               hideNodeNames={brokenNodeNames}