revert(startup): keep open-scrobble sweep deferred for fast startup

Reverts 7161c86f. Running the sweep synchronously before the listener could
add up to 30s to restart-before-playback when a watch provider is
unreachable, which regresses the deliberate startup-deferral from dfa0f686.
Prefer the fast-startup behavior and accept the small window where a resume
immediately after restart may create a duplicate scrobble; the sweep returns
to the deferred background-init list. (Panic-safety for that list is added in
a follow-up commit.)

Per PR #21 review decision.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cmd/silo/main.go

@@ -1023,6 +1023,11 @@ func main() {
 			WithMatcher(historyimport.NewMatcher(historyRepo)).
 			WithWatchState(watchstate.NewService(userStoreProvider).WithStableIdentityResolver(historyIdentity)).
 			WithUserStoreProvider(userStoreProvider)
+		backgroundInit = append(backgroundInit, func(ctx context.Context) {
+			if err := watchProviderService.SweepOpenScrobbles(ctx); err != nil {
+				slog.Warn("failed to sweep open watch provider scrobbles", "error", err)
+			}
+		})
 	}
 	deps.SessionMgr = sessionMgr
 	deps.PlaybackRealtimeHub = playback.NewRealtimeHub()
@@ -1678,19 +1683,6 @@ func main() {
 		}()
 	}
 
-	// Stop scrobble sessions left open by the previous process BEFORE the
-	// listener accepts playback requests, so a resume immediately after a
-	// restart doesn't create overlapping/stale scrobbles on remote providers.
-	// Bounded by a timeout so an unreachable provider can't hang startup (which
-	// is why the rest of non-critical init stays deferred below).
-	if watchProviderService != nil {
-		sweepCtx, cancelSweep := context.WithTimeout(appCtx, 30*time.Second)
-		if err := watchProviderService.SweepOpenScrobbles(sweepCtx); err != nil {
-			slog.Warn("failed to sweep open watch provider scrobbles", "error", err)
-		}
-		cancelSweep()
-	}
-
 	errCh := make(chan error, 2)
 	go func() {
 		slog.Info("HTTP server listening", "addr", cfg.Server.Listen)