{# Header — gains a festive gradient when fun mode is on; goes full
rainbow when the user shift-clicks into ultra. #}
{# Scope bar — persistent indicator of which corpus the agent searches.
On episode pages it's a segmented control; on channel pages it's a
static badge so the user always knows what the chat is grounded in. #}
{# So the user never has to guess whether their playful preference
is active — the tiny header pill alone was easy to miss. Ultra
mode swaps to a rainbow strip + louder copy. #}