Add !post command to force-publish next queued story

Typed in a configured channel room, !post pops the head of that channel's
queue and sends immediately, bypassing min-interval, burst cap, and daily
cap. Canonical-URL dedup still applies. Empty queue gets a threaded reply.

internal/poster/queue.go

@@ -90,6 +90,26 @@ func (q *Queue) Wait() {
 	<-q.done
 }
 
+// ForcePost pops the next queued item for the given channel and posts it
+// immediately, bypassing min-interval, burst cap, and daily cap. Dedup
+// (canonical URL cooldown) still applies. Returns true if an item was sent.
+func (q *Queue) ForcePost(channel string) bool {
+	q.mu.Lock()
+	items := q.queues[channel]
+	if len(items) == 0 {
+		q.mu.Unlock()
+		return false
+	}
+	item := items[0]
+	q.queues[channel] = items[1:]
+	q.mu.Unlock()
+
+	slog.Info("force-posting story on demand",
+		"guid", item.GUID, "channel", channel)
+	q.postItem(item)
+	return true
+}
+
 func (q *Queue) drain() {
 	q.mu.Lock()
 	channels := make([]string, 0, len(q.queues))