Force zarr v2 compatibility for xarray

- Use zarr_version=2 parameter in xr.open_zarr()
- Enable consolidated metadata
- Fixes GroupNotFoundError with zarr v3 API

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app.py

@@ -61,7 +61,8 @@ def load_dataset(dataset_name, use_cache=True):
         url = CATALOG[dataset_name]["url"]
         logger.info(f"Opening zarr store at: {url}")
 
-        ds = xr.open_zarr(url)
+        # Try opening with zarr_version=2 for compatibility
+        ds = xr.open_zarr(url, zarr_version=2, consolidated=True)
         logger.info(f"Successfully opened zarr store")
         logger.info(f"Dataset dimensions: {dict(ds.dims)}")
         logger.info(f"Dataset variables: {list(ds.data_vars)}")