feat: eliminar actividad, bloqueado si tiene tareas pendientes

No existia forma de borrar una actividad. Agregado DELETE
/api/activities/:id con boton "Eliminar" en el listado (popup de
confirmacion). Si tiene tareas, se bloquea con 400 y mensaje claro en
vez de arrastrar todo en cascada sin avisar.

De paso: la logica de borrar adjunto (fila + archivo en disco) se
extrajo a un attachments/service.js reutilizable, usado tanto por el
borrado individual como por el borrado en cascada de una actividad
(evita archivos huerfanos). Comentarios de la actividad tambien se
limpian (sin FK fisica cruzada, entity_type/entity_id es polimorfico).

Probado en dev con curl (bloquea con tarea, permite sin tareas, 404
tras borrar) y Playwright (mensaje de advertencia visible).

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

frontend/src/pages/Proyectos/ProjectActivitiesTab.jsx

@@ -1,8 +1,9 @@
 import { useState } from 'react';
-import { Plus, Save } from 'lucide-react';
+import { Plus, Save, Trash2 } from 'lucide-react';
 import { useUi } from '../../context/ui-context.jsx';
+import { useAuth } from '../../context/auth-context.jsx';
 import { useAsync, useAction } from '../../hooks/useAsync.js';
-import { listActivitiesByProject, createActivity, getActivity } from '../../services/activities.js';
+import { listActivitiesByProject, createActivity, getActivity, deleteActivity } from '../../services/activities.js';
 import { listCatalog } from '../../services/catalogs.js';
 import { listUsers } from '../../services/users.js';
 import { ListView } from '../../components/ListView.jsx';
@@ -18,7 +19,8 @@ import ActivityDetailPanel from './ActivityDetailPanel.jsx';
 const EMPTY_FORM = { name: '', description: '', responsibleUserId: '', priorityId: '', statusId: '', startDate: '', dueDate: '', isMilestone: false };
 
 export default function ProjectActivitiesTab({ projectId }) {
-  const { t, pushToast } = useUi();
+  const { t, pushToast, openDialog } = useUi();
+  const { user: currentUser } = useAuth();
   const runAction = useAction();
   const { data: activities, reload } = useAsync(() => listActivitiesByProject(projectId), [projectId]);
   const { data: priorities } = useAsync(() => listCatalog('priorities'), []);
@@ -55,6 +57,25 @@ export default function ProjectActivitiesTab({ projectId }) {
     if (selected) setSelected(await getActivity(selected.id));
   }
 
+  function confirmDelete(row) {
+    openDialog({
+      tone: 'warning',
+      title: t('common_confirm_delete_title'),
+      message: t('common_confirm_delete_msg'),
+      actions: [
+        { label: t('common_cancel'), variant: 'standard' },
+        {
+          label: t('common_delete'), variant: 'danger',
+          onClick: () => runAction(async () => {
+            await deleteActivity(row.id);
+            await reload();
+            pushToast({ tone: 'success', message: t('common_saved') });
+          }),
+        },
+      ],
+    });
+  }
+
   const columns = [
     { key: 'code', label: t('activity_code') },
     { key: 'name', label: t('common_name') },
@@ -86,6 +107,9 @@ export default function ProjectActivitiesTab({ projectId }) {
         getSearchHaystack={(a) => `${a.code} ${a.name} ${a.responsible_name || ''}`}
         getRowKey={(a) => a.id}
         onRowClick={openActivity}
+        rowActions={currentUser?.roleCode !== 'viewer' ? (a) => [
+          { label: t('common_delete'), icon: Trash2, danger: true, onClick: () => confirmDelete(a) },
+        ] : undefined}
       />
 
       <DetailPopup open={creating} title={t('activity_new')} onClose={() => setCreating(false)} width={640} height={560}>