index: a reset burn store never recounts the scrobbles the view already holds #100

On the token-burn stack (#231): the burn store is fed only by announced events (service.rs, announce_from → burn.observe), and the view announces nothing for a scrobble it already holds (view.rs, take_scrobble). So when the store starts empty while --state keeps the view, a store version bump (the store is now version 2, and an older one is let go), a lost or corrupt --burn file, or a new --burn path, every scrobble the view holds is never counted, and only later ones are. Seeding the store from the view's held scrobbles at start-up, through the same Window::of path, would close that gap. Related: #61 (the store is not backed up) and #63 (windows missed while offline).