feat: soporte de threads de Matrix (m.thread)

Implementa el soporte completo de threads de Matrix:
- Listener extrae ThreadID de m.relates_to con rel_type=m.thread
- Client.SendThreadMarkdown envia mensajes como parte de un thread
  usando SetThread de mautrix con fallback m.in_reply_to
- Runner detecta ThreadID en ReplyAction y rutea a SendThreadMarkdown
- MatrixSender interfaz actualizada con SendThreadMarkdown
- runtime.go propaga ThreadID en todas las respuestas (comandos, LLM, RBAC)
- sendReply helper centraliza la logica de envio con/sin thread
- Auto-thread: si matrix.threads.auto_thread=true, crea thread nuevo
  para cada conversacion que no esta ya en un thread
- Memoria por thread: usa ThreadID como clave de window cuando el mensaje
  esta en un thread, permitiendo conversaciones paralelas independientes
- Config: matrix.threads.enabled y matrix.threads.auto_thread en ThreadsCfg

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shell/effects/runner.go

@@ -24,6 +24,7 @@ type MatrixSender interface {
 	SendText(ctx context.Context, roomID, text string) error
 	SendMarkdown(ctx context.Context, roomID, markdown string) error
 	SendReplyMarkdown(ctx context.Context, roomID, inReplyTo, markdown string) error
+	SendThreadMarkdown(ctx context.Context, roomID, threadRootID, inReplyTo, markdown string) error
 	SendTyping(ctx context.Context, roomID string, typing bool) error
 }
 
@@ -63,15 +64,15 @@ func (r *Runner) executeOne(ctx context.Context, roomID string, a decision.Actio
 		if a.Reply == nil {
 			return Result{Action: a, Err: fmt.Errorf("nil reply action")}
 		}
-		target := roomID
-		if a.Reply.ThreadID != "" {
-			target = a.Reply.ThreadID
-		}
 		var err error
-		if a.Reply.InReplyTo != "" {
-			err = r.matrix.SendReplyMarkdown(ctx, target, a.Reply.InReplyTo, a.Reply.Content)
-		} else {
-			err = r.matrix.SendMarkdown(ctx, target, a.Reply.Content)
+		switch {
+		case a.Reply.ThreadID != "":
+			// Thread reply: send as part of the thread with fallback in_reply_to
+			err = r.matrix.SendThreadMarkdown(ctx, roomID, a.Reply.ThreadID, a.Reply.InReplyTo, a.Reply.Content)
+		case a.Reply.InReplyTo != "":
+			err = r.matrix.SendReplyMarkdown(ctx, roomID, a.Reply.InReplyTo, a.Reply.Content)
+		default:
+			err = r.matrix.SendMarkdown(ctx, roomID, a.Reply.Content)
 		}
 		return Result{Action: a, Output: a.Reply.Content, Err: err}