merge: quick/fix-thread-send-pointer — fix m.relates_to en eventos cifrados de thread

Corrige el bug por el que el agente enviaba respuestas de thread sin m.relates_to en el evento m.room.encrypted exterior. mautrix-go usaba getRelatesTo() que requiere pointer receiver, pero se pasaba el content por valor. Element Web no podia detectar la relacion de thread y mostraba la respuesta en la timeline principal.

shell/matrix/client.go

@@ -276,7 +276,7 @@ func (c *Client) SendText(ctx context.Context, roomID, text string) error {
 // FormattedBody contains the HTML rendered by goldmark.
 func (c *Client) SendMarkdown(ctx context.Context, roomID, markdown string) error {
 	html := mdToHTML(markdown)
-	content := event.MessageEventContent{
+	content := &event.MessageEventContent{
 		MsgType:       event.MsgText,
 		Body:          markdown,
 		Format:        event.FormatHTML,
@@ -309,7 +309,7 @@ func mdToHTML(md string) string {
 // It sets m.in_reply_to so Matrix clients show the original message as a quote.
 func (c *Client) SendReplyMarkdown(ctx context.Context, roomID, inReplyTo, markdown string) error {
 	html := mdToHTML(markdown)
-	content := event.MessageEventContent{
+	content := &event.MessageEventContent{
 		MsgType:       event.MsgText,
 		Body:          markdown,
 		Format:        event.FormatHTML,
@@ -329,7 +329,10 @@ func (c *Client) SendThreadMarkdown(ctx context.Context, roomID, threadRootID, i
 		inReplyTo = threadRootID
 	}
 	html := mdToHTML(markdown)
-	content := event.MessageEventContent{
+	// Must use a pointer so mautrix-go can call OptionalGetRelatesTo() (pointer receiver)
+	// and copy m.relates_to to the outer m.room.encrypted event. Without this, Element
+	// Web does not see the thread relationship and shows the reply in the main timeline.
+	content := &event.MessageEventContent{
 		MsgType:       event.MsgText,
 		Body:          markdown,
 		Format:        event.FormatHTML,