3a4e17c735
Creator on the live build: 'why do you make the youtube user icon go away?'
The TASK 42 one-surface bar had scoped the account zone to Stream only
('Record world has no YouTube identity at all'), so arming REC dropped the
avatar and the bar height bounced with it ('really fucking annoying').
Fix: ShowSignInButton / ShowAvatarButton are now plain !IsConnected /
IsConnected — app-level identity, present in both worlds, so the right
column never pops in/out and the bar height stays pinned. Test remains a
child of Stream (still stream-armed AND signed-in).
TopBarModeTests updated to the new contract: signed-out Record world shows
Sign In; flipping back to REC keeps the avatar. PillRadioTests untouched
(it only exercises the ON-AIR face). Docs corrected in-place (ai.md state
model, TASK 42 scope). Gate: clean build 0-warnings, 316/316, scope passed.