FWHM across field of view

e.g. after the chimney plot -- to invite for exploration
```
plt.figure()
plt.scatter(
    ref_catalog["xcentroid_win"], 
    ref_catalog["ycentroid_win"], 
    c=ref_photo_cat["fwhm_fit"],
    vmin=5.0, vmax=9.0,
    cmap="jet",
    s=10
)
plt.colorbar(label="FWHM from fit [pix]")
plt.xlabel("x [pix]")
plt.ylabel("y [pix]")
plt.tight_layout()
plt.show()

```