Two fixes to how online status is handled during registration:
1. Re-registration (applyAuthNodeUpdate, HandleNodeFromPreAuthKey) no
longer resets IsOnline to false. Online status is managed exclusively
by Connect()/Disconnect() in the poll session lifecycle. The reset
caused a false offline blip: the auth handler's change notification
triggered a map regeneration showing the node as offline to peers,
even though Connect() would set it back to true moments later.
2. New node creation (createAndSaveNewNode) now explicitly sets
IsOnline=false instead of leaving it nil. This ensures peers always
receive a known online status rather than an ambiguous nil/unknown.
1053fbb16b