feat: contador de Tareas muestra pendientes/total (ej. 2/3)

Solo la pestaña Tareas -- Comentarios y Documentos siguen con el total simple. Se recalcula al
agregar, quitar o marcar/desmarcar tareas.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/pages/Proyectos/ActivityDetailPanel.jsx

@@ -59,7 +59,11 @@ export default function ActivityDetailPanel({ activity, projectId, siblingActivi
   useEffect(() => { setForm(toForm(activity)); setEditing(false); }, [activity]);
 
   const hasTasks = tasks && tasks.length > 0;
+  const totalTasksCount = (tasks || []).length;
   const pendingTasksCount = (tasks || []).filter((task) => !task.is_done).length;
+  // "pendientes/total" (ej. "2/3") en vez de un numero solo — cambia solo cuando se agregan,
+  // quitan o marcan/desmarcan tareas.
+  const tasksTabCount = totalTasksCount > 0 ? `${pendingTasksCount}/${totalTasksCount}` : 0;
   const priorityOptions = (priorities || []).map((p) => ({ value: p.id, label: p.name }));
   const statusOptions = (statuses || []).map((s) => ({ value: s.id, label: s.name }));
   const userOptions = (users || []).map((u) => ({ value: u.id, label: u.name }));
@@ -148,7 +152,7 @@ export default function ActivityDetailPanel({ activity, projectId, siblingActivi
       <Tabs
         tabs={[
           { key: 'detail', label: t('tab_info') },
-          { key: 'tasks', label: t('tasks_title'), count: pendingTasksCount },
+          { key: 'tasks', label: t('tasks_title'), count: tasksTabCount },
           { key: 'dependencies', label: t('activity_dependencies') },
           { key: 'comments', label: t('tab_comments'), count: (comments || []).length },
           { key: 'documents', label: t('tab_documents'), count: (attachments || []).length },