Add posting.enabled master switch to disable auto-posting to Matrix

Stories are still ingested, classified, and served to the web UI; only
automatic Matrix posting is gated. Command replies (!post, !petestats)
still work. Pointer-bool so an absent key defaults to posting-on.

main.go

@@ -174,7 +174,11 @@ func main() {
 	go queue.Start(ctx)
 	slog.Info("post queue started")
 
+	postingEnabled := *cfg.Posting.Enabled
 	roundRobinMode := cfg.Posting.RoundRobin.Enabled
+	if !postingEnabled {
+		slog.Info("automatic Matrix posting is disabled (posting.enabled=false); stories will still be ingested and served to the web UI, and !post still works")
+	}
 
 	// Pipeline callback: route the story to its direct_route channel, then
 	// either enqueue immediately or leave it for the round-robin scheduler.
@@ -188,6 +192,12 @@ func main() {
 		channel := item.DirectRoute
 		storage.MarkClassified(item.GUID, channel, "[]")
 
+		// Posting disabled: classify and keep for the web UI / manual !post,
+		// but never auto-enqueue to Matrix.
+		if !postingEnabled {
+			return
+		}
+
 		if roundRobinMode {
 			slog.Info("story routed, awaiting round-robin tick",
 				"guid", item.GUID, "source", item.Source, "channel", channel)
@@ -215,7 +225,7 @@ func main() {
 	poller.Start(ctx)
 	slog.Info("pollers started")
 
-	if roundRobinMode {
+	if postingEnabled && roundRobinMode {
 		channelNames := make([]string, 0, len(cfg.Matrix.Channels))
 		for name := range cfg.Matrix.Channels {
 			channelNames = append(channelNames, name)