Syncs the us4us card and figures on the Hub with the reviewed state on GitHub (open-h/OpenH-RF).
One correction: the card said every file holds 10 slices except the water reference. `yezitronix-b-rg-1.2.hdf5` holds 11, `reference_water.hdf5` holds one, and the forearm files hold 10.
Adds the figure the card now leads with, `assets/s1_l_reconstruct.png`: slice 8 of `data/s1_l.hdf5`, a left-forearm cross-section reconstructed by `reconstruct.py` beside the sinogram and reference image stored in the file. The card gains a title, that figure, and a Data Validation line saying how to reproduce it (set `ZEA_FILE` and `FRAME` at the top of the script). `assets/main.png` is the release image and is not embedded in the card.
Files changed: 3.
```
+ us4us/assets/main.png
+ us4us/assets/s1_l_reconstruct.png
~ us4us/README.md
```
