feat: implement queue pruning and message rotation

Enforce QUEUE_MAX_AGE and MAX_HISTORY config values that previously
existed but were not applied. The existing cleanup loop now also:

- Prunes client_queues entries older than QUEUE_MAX_AGE (default 48h)
- Rotates messages per target (channel/DM) beyond MAX_HISTORY (default 10000)
- Removes orphaned messages no longer referenced by any client queue

closes #40

internal/handlers/handlers.go

@@ -200,4 +200,63 @@ func (hdlr *Handlers) runCleanup(
 			"deleted", deleted,
 		)
 	}
+
+	hdlr.pruneQueuesAndMessages(ctx)
+}
+
+// pruneQueuesAndMessages removes old client_queues entries
+// per QUEUE_MAX_AGE, rotates messages per MAX_HISTORY, and
+// cleans up orphaned messages.
+func (hdlr *Handlers) pruneQueuesAndMessages(
+	ctx context.Context,
+) {
+	queueMaxAge := hdlr.params.Config.QueueMaxAge
+	if queueMaxAge > 0 {
+		queueCutoff := time.Now().Add(
+			-time.Duration(queueMaxAge) * time.Second,
+		)
+
+		pruned, err := hdlr.params.Database.
+			PruneOldQueueEntries(ctx, queueCutoff)
+		if err != nil {
+			hdlr.log.Error(
+				"queue pruning failed", "error", err,
+			)
+		} else if pruned > 0 {
+			hdlr.log.Info(
+				"pruned old queue entries",
+				"deleted", pruned,
+			)
+		}
+	}
+
+	maxHistory := hdlr.params.Config.MaxHistory
+	if maxHistory > 0 {
+		rotated, err := hdlr.params.Database.
+			RotateChannelMessages(ctx, maxHistory)
+		if err != nil {
+			hdlr.log.Error(
+				"message rotation failed", "error", err,
+			)
+		} else if rotated > 0 {
+			hdlr.log.Info(
+				"rotated old messages",
+				"deleted", rotated,
+			)
+		}
+	}
+
+	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,
+		)
+	}
 }