In Teams, the shortcut is Shift+Enter. Try that — it should create a linebreak for you.
Also, you can always just click the little “A” in the compose box (on the lower left side of the compose box) to expand the compose box, and this turns the “Enter” key into a line break.
Yes, be consistent with the option in Skype:
Use Ctrl or Shift or Alt + Enter to send
The Registry location now seems to be TeamsAddin.Connect instead of TeamsAddin.FastConnect, but do both to be safe.
Also, if you want to stop "Skype Meeting Add-in for Microsoft Office" (also added upon running Teams, despite the DLL being part of Office!), its name is UCAddin.LyncAddin.1.
Yes, why does this happen? I thought it was just upon Teams upgrade, but no, simply upon launch.
It also adds the Skype Meeting Add-in for Microsoft Office somehow, even though it's not part of teams but rather Office 2016/365.
It does now, but I wish it didn't.
This is still under review by the feature team. No new details yet.