At some point over the last few days, Apple quietly removed the Photos app from the iCloud website. The app itself is still in the beta stages, but the exact reason why Apple removed the app is still unknown.
It may remain unknown, too, considering that, as of the time of this writing, it has been confirmed that the Photos app has been returned to the iCloud website, both in the public facing form and the beta iCloud.com. The app’s icon is now present on the homepage yet again, but clicking into it seems to bring up the fully-functioning app as well. That includes the ability to directly upload photos through the iCloud website, which was added in early November of this year.
Have you used the Photos app on iCloud.com yet?