REPL and fleet view read from a shared snapshot instead of scattered state

Streaming state, including the user's input while a turn is processing, the streaming text peek, the interruptible-tool flag, a pending preserved insert and the API metrics reset, moves onto one stream object. The message queue is now passed explicitly to spawn and notification paths rather than reached through a module-level function, and the fleet view drops eight initial-state props in favour of snapshot reads for focused index, rename state, follow origin and mode. No behaviour change is claimed, though most REPL callback signatures changed.