refactor: 30-day defaults, time-based message expiry

- Change QUEUE_MAX_AGE default from 48h to 30 days (2592000s)
- Replace count-based MAX_HISTORY with time-based MESSAGE_MAX_AGE
  (default 30 days) — messages older than the configured age are
  pruned instead of keeping a fixed count per target
- Update README to reflect new defaults and time-based expiry

internal/handlers/handlers.go

@@ -205,8 +205,7 @@ func (hdlr *Handlers) runCleanup(
 }
 
 // pruneQueuesAndMessages removes old client_queues entries
-// per QUEUE_MAX_AGE, rotates messages per MAX_HISTORY, and
-// cleans up orphaned messages.
+// per QUEUE_MAX_AGE and old messages per MESSAGE_MAX_AGE.
 func (hdlr *Handlers) pruneQueuesAndMessages(
 	ctx context.Context,
 ) {
@@ -230,18 +229,22 @@ func (hdlr *Handlers) pruneQueuesAndMessages(
 		}
 	}
 
-	maxHistory := hdlr.params.Config.MaxHistory
-	if maxHistory > 0 {
-		rotated, err := hdlr.params.Database.
-			RotateChannelMessages(ctx, maxHistory)
+	messageMaxAge := hdlr.params.Config.MessageMaxAge
+	if messageMaxAge > 0 {
+		msgCutoff := time.Now().Add(
+			-time.Duration(messageMaxAge) * time.Second,
+		)
+
+		pruned, err := hdlr.params.Database.
+			PruneOldMessages(ctx, msgCutoff)
 		if err != nil {
 			hdlr.log.Error(
-				"message rotation failed", "error", err,
+				"message pruning failed", "error", err,
 			)
-		} else if rotated > 0 {
+		} else if pruned > 0 {
 			hdlr.log.Info(
-				"rotated old messages",
-				"deleted", rotated,
+				"pruned old messages",
+				"deleted", pruned,
 			)
 		}
 	}