I would say a login screen would be a little out of reach when you're unable to get a global HUD to display, but I digress. I can at least help with your first problem! I have no experience with the websockets in Construct.
To build a UI that tags along onto each Layout you'll want to set the object to be global, and possibly set their behaviour to Anchor to make sure they stick to the same place when the screen scrolls. The following tutorial should give you a decent idea of how to make a basic global UI: https://www.scirra.com/tutorials/594/bu ... terface-ui
Of course, if you only wish to know how to make an object global (i.e. it traverses through every layout that comes AFTER the one it has been made on) the following image should help:
That image comes from the object properties in the layout editor. (Courtesy of the aforementioned tutorial)