Legend (categorical obs column) for scatterplot widget not consistent

Originally discovered here: https://github.com/scverse/napari-spatialdata/issues/328#issuecomment-2464885435.

To reproduce:

import numpy as np
import scanpy as sc

from spatialdata.datasets import blobs

np.random.seed(10)

sdata = blobs(length=1000, n_channels=3)

sc.pp.pca(
    sdata["table"],
    copy=False,
)

sc.pp.neighbors(
    sdata["table"],
    copy=False,
)
sc.tl.umap(
    sdata["table"],
    copy=False,
)

sdata["table"].obs["new_category"] = np.random.randint(0, 15, size=len(sdata["table"].obs))
sdata["table"].obs["new_category"] = sdata["table"].obs["new_category"].astype("category")

sc.pl.umap(sdata.tables["table"], color=["new_category"], show=True)


from napari_spatialdata import Interactive

Interactive(sdata)

Finally, open the scatterplot widget and make the UMAP as below (you need to open the labels layer first, since it is the one annotated by the table.

This is what is given (the two plots should have the same colors, but they don't).

Run the provided Python reproduction with spatialdata.datasets.blobs and the napari-spatialdata Interactive entry point, then open the scatterplot widget for the categorical obs column. Compare its legend and colors with the sc.pl.umap output. Done means both plots use the same categorical colors and legend mapping.