fix(world): centralize shadow config and remove warmup

- Extract SHADOW_CONFIG into lightingConfig.ts (bias=0, normalBias=0,
  cameraSize=95) matching the historically working values from develop.
- Drop SceneShadowWarmup; rely on sun.shadow.autoUpdate=true for
  steady-state refresh.
- Enable cloud castShadow and traverse Ebike meshes for cast/receive.

src/components/ebike/Ebike.tsx

@@ -131,6 +131,17 @@ export function Ebike({ position }: EbikeProps): React.JSX.Element {
     }
   }, [model]);
 
+  useEffect(() => {
+    if (!model) return;
+
+    model.traverse((child) => {
+      if (child instanceof THREE.Mesh) {
+        child.castShadow = true;
+        child.receiveShadow = true;
+      }
+    });
+  }, [model]);
+
   useEffect(() => {
     window.ebikeVisualGroup = groupRef;
     window.ebikeParkedPosition = restingPositionRef.current;