fix: address PR #662 review comments (bus drain, context timeouts, onebot leak)

- Drain buffered messages in MessageBus.Close() so they aren't silently lost
- Replace all context.TODO() with context.WithTimeout(5s) across 7 call sites
- Fix OneBot pending channel leak: send nil sentinel in Stop() and handle
  nil response in sendAPIRequest() to unblock waiting goroutines

pkg/tools/cron.go

@@ -294,7 +294,9 @@ func (t *CronTool) ExecuteJob(ctx context.Context, job *cron.CronJob) string {
 			output = fmt.Sprintf("Scheduled command '%s' executed:\n%s", job.Payload.Command, result.ForLLM)
 		}
 
-		t.msgBus.PublishOutbound(context.TODO(), bus.OutboundMessage{
+		pubCtx, pubCancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer pubCancel()
+		t.msgBus.PublishOutbound(pubCtx, bus.OutboundMessage{
 			Channel: channel,
 			ChatID:  chatID,
 			Content: output,
@@ -304,7 +306,9 @@ func (t *CronTool) ExecuteJob(ctx context.Context, job *cron.CronJob) string {
 
 	// If deliver=true, send message directly without agent processing
 	if job.Payload.Deliver {
-		t.msgBus.PublishOutbound(context.TODO(), bus.OutboundMessage{
+		pubCtx, pubCancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer pubCancel()
+		t.msgBus.PublishOutbound(pubCtx, bus.OutboundMessage{
 			Channel: channel,
 			ChatID:  chatID,
 			Content: job.Payload.Message,