Refactor Xenium + Visium paths and use better names

• all the paths used in notebooks 00_xenium_and_visium.ipynb, 01_xenium_and_visium.ipynb and 02_xenium_and_visium.ipynb should be placed in a config.py file
• sandbox.zarr was a poorly chosen name, rename it to manual_annotations.zarr. I have already made a copy in the S3 bucket of that file (so that now both sandbox.zarr.zip and manual_annotations.zarr.zip are present), so one needs just to adjust the notebooks.

从 00_xenium_and_visium.ipynb、01_xenium_and_visium.ipynb 和 02_xenium_and_visium.ipynb 中的路径开始，然后检查 config.py 应如何保存这些路径。更新 notebooks，使其使用 manual_annotations.zarr 而不是 sandbox.zarr，并验证所有路径都已集中管理，且引用的是重命名后的 S3 副本。