fix: remove PruneOrphanedMessages to preserve history within MAX_HISTORY

PruneOrphanedMessages deleted messages that lost their client_queues
references after PruneOldQueueEntries ran, even when those messages
were within the MAX_HISTORY limit. This made MAX_HISTORY meaningless
for low-traffic channels.

RotateChannelMessages already caps messages per target. Queue pruning
handles client_queues growth. Orphan cleanup is redundant.

Closes #40

internal/handlers/handlers.go

@@ -245,18 +245,4 @@ func (hdlr *Handlers) pruneQueuesAndMessages(
 			)
 		}
 	}
-
-	orphaned, err := hdlr.params.Database.
-		PruneOrphanedMessages(ctx)
-	if err != nil {
-		hdlr.log.Error(
-			"orphan message cleanup failed",
-			"error", err,
-		)
-	} else if orphaned > 0 {
-		hdlr.log.Info(
-			"pruned orphaned messages",
-			"deleted", orphaned,
-		)
-	}
 }