Feature request: add a sample file to the upload menu

If a user (or tester, such as, for example, me) wanted to play around with the IC, or quickly check or try something, it would be useful for them to have a pre-uploaded sample file that they could open without uploading resources. I think it's ok if the sample file doesn't have training data, just an image and its corresponding json file. We could have one sample file for Hufnagel, and one for square notation.

Perhaps these for Hufnagel:

[NZ-Wt MSR-03 013r.zip](https://github.com/user-attachments/files/29749587/NZ-Wt.MSR-03.013r.zip)

And these for square notation:

[CDN-Hsmu_M2149.L4_024r.zip](https://github.com/user-attachments/files/29750637/CDN-Hsmu_M2149.L4_024r.zip)