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/matrix/client.go

@@ -29,6 +29,10 @@ import (
 // ReactionHandler is called when a reaction is received on a post.
 type ReactionHandler func(roomID id.RoomID, eventID id.EventID, targetEventID id.EventID, emoji string, userID id.UserID)
 
+// MessageHandler is called when a text message is received in a configured room.
+// body is the plain-text content; channel is the configured channel name for the room.
+type MessageHandler func(channel string, roomID id.RoomID, eventID id.EventID, sender id.UserID, body string)
+
 // deviceInfo holds persisted device credentials.
 type deviceInfo struct {
 	AccessToken string `json:"access_token"`
@@ -47,6 +51,7 @@ type Client struct {
 
 	mu         sync.RWMutex
 	onReact    ReactionHandler
+	onMessage  MessageHandler
 	cancelSync context.CancelFunc
 }
 
@@ -217,6 +222,23 @@ func (c *Client) SetReactionHandler(fn ReactionHandler) {
 	c.onReact = fn
 }
 
+// SetMessageHandler registers a callback for text messages in configured channel rooms.
+func (c *Client) SetMessageHandler(fn MessageHandler) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.onMessage = fn
+}
+
+// ChannelForRoom returns the channel name configured for the given room, if any.
+func (c *Client) ChannelForRoom(roomID id.RoomID) (string, bool) {
+	for name, rid := range c.channels {
+		if rid == roomID {
+			return name, true
+		}
+	}
+	return "", false
+}
+
 // Start begins the Matrix sync loop in the background.
 func (c *Client) Start(ctx context.Context) {
 	syncer := c.mx.Syncer.(*mautrix.DefaultSyncer)
@@ -247,6 +269,27 @@ func (c *Client) Start(ctx context.Context) {
 		}
 	})
 
+	// Listen for text messages in configured channel rooms
+	syncer.OnEventType(event.EventMessage, func(ctx context.Context, evt *event.Event) {
+		if evt.Sender == c.userID {
+			return
+		}
+		channel, ok := c.ChannelForRoom(evt.RoomID)
+		if !ok {
+			return
+		}
+		msg := evt.Content.AsMessage()
+		if msg == nil || msg.MsgType != event.MsgText {
+			return
+		}
+		c.mu.RLock()
+		handler := c.onMessage
+		c.mu.RUnlock()
+		if handler != nil {
+			handler(channel, evt.RoomID, evt.ID, evt.Sender, msg.Body)
+		}
+	})
+
 	// Auto-join on invite
 	syncer.OnEventType(event.StateMember, func(ctx context.Context, evt *event.Event) {
 		if evt.GetStateKey() == string(c.userID) && evt.Content.AsMember().Membership == event.MembershipInvite {