feat: historial de cambios (usuario, fecha, detalle)

Tabla change_history, pantalla en Agencia OS y registro automático
al guardar o enriquecer Zona de marca.

Co-authored-by: Cursor <cursoragent@cursor.com>

sql/change_history.sql

@@ -0,0 +1,35 @@
+-- Historial de cambios del Centro de Mando (agencia + cliente).
+-- Idempotente.
+
+create table if not exists public.change_history (
+  id uuid primary key default gen_random_uuid(),
+  tenant_id uuid references public.tenants(id) on delete set null,
+  tenant_name text,
+  user_id uuid,
+  user_email text not null default 'sistema',
+  user_role text,
+  entity_type text not null,
+  entity_id text,
+  action text not null,
+  summary text not null,
+  detail jsonb not null default '{}'::jsonb,
+  source text,
+  created_at timestamptz not null default now()
+);
+
+create index if not exists change_history_created_idx
+  on public.change_history (created_at desc);
+
+create index if not exists change_history_tenant_created_idx
+  on public.change_history (tenant_id, created_at desc);
+
+create index if not exists change_history_entity_idx
+  on public.change_history (entity_type, created_at desc);
+
+comment on table public.change_history is
+  'Auditoría de cambios: usuario, fecha, acción y detalle (Zona de marca, creatividades, etc.)';
+
+alter table public.change_history enable row level security;
+
+-- Solo service role escribe/lee vía API (Centro de Mando). Sin policies abiertas.
+drop policy if exists change_history_agency_read on public.change_history;