feat: mensajes progresivos en Matrix con ProgressReporter

Implementa la Fase 2 del issue 0036: mensajes de progreso en tiempo real
que muestran al usuario que herramientas esta usando el agente claude-code.

- SendMarkdownGetID en shell/matrix/client.go: envia mensaje y retorna
  el event ID para editarlo despues
- EditMessage en shell/matrix/client.go: edita un mensaje existente
  usando m.replace (m.relates_to con rel_type=m.replace)
- ProgressReporter en shell/effects/progress.go (NEW): recibe streaming
  events y actualiza un mensaje unico en Matrix mostrando el progreso
  (e.g. "🔧 Bash: ls -la" → "🔧 Read: file.go" → "✅ Completado")
- Rate limiter integrado: max 1 edit/segundo para no saturar el homeserver
- Conectado en devagents/handler.go: cuando provider=claude-code y
  streaming+show_tool_progress habilitados, crea ProgressReporter y
  pasa StreamFunc al CompletionRequest
- MatrixSender interface actualizada con los nuevos metodos
- 10 tests nuevos para ProgressReporter, todos los existentes pasan

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shell/matrix/client.go

@@ -286,6 +286,51 @@ func (c *Client) SendMarkdown(ctx context.Context, roomID, markdown string) erro
 	return err
 }
 
+// SendMarkdownGetID sends a formatted (Markdown) message to a room and returns
+// the event ID of the sent message. Useful for later editing via EditMessage.
+func (c *Client) SendMarkdownGetID(ctx context.Context, roomID, markdown string) (string, error) {
+	html := mdToHTML(markdown)
+	content := &event.MessageEventContent{
+		MsgType:       event.MsgText,
+		Body:          markdown,
+		Format:        event.FormatHTML,
+		FormattedBody: html,
+	}
+	resp, err := c.raw.SendMessageEvent(ctx, id.RoomID(roomID), event.EventMessage, content)
+	if err != nil {
+		return "", err
+	}
+	return resp.EventID.String(), nil
+}
+
+// EditMessage edits a previously sent message in a room using m.replace relation.
+// originalEventID is the event ID of the message to replace.
+// The new content is rendered from markdown.
+func (c *Client) EditMessage(ctx context.Context, roomID, originalEventID, markdown string) error {
+	html := mdToHTML(markdown)
+
+	// Matrix spec: m.new_content holds the replacement, m.relates_to with
+	// rel_type=m.replace points to the original event.
+	content := &event.MessageEventContent{
+		MsgType:       event.MsgText,
+		Body:          "* " + markdown, // per spec: prefix with "* " for fallback
+		Format:        event.FormatHTML,
+		FormattedBody: "* " + html,
+		RelatesTo: &event.RelatesTo{
+			Type:    event.RelReplace,
+			EventID: id.EventID(originalEventID),
+		},
+		NewContent: &event.MessageEventContent{
+			MsgType:       event.MsgText,
+			Body:          markdown,
+			Format:        event.FormatHTML,
+			FormattedBody: html,
+		},
+	}
+	_, err := c.raw.SendMessageEvent(ctx, id.RoomID(roomID), event.EventMessage, content)
+	return err
+}
+
 // mdToHTML converts a Markdown string to HTML using goldmark with full extensions.
 var mdParser = goldmark.New(
 	goldmark.WithExtensions(