feat(panel): add sponsor slots fed from sponsors.sanaei.dev

Monthly sponsor placements need to change without cutting a panel
release. Panels now read 3X/sponsors.json from the MHSanaei/sponsors
repo (GitHub Pages on sponsors.sanaei.dev) and show active sponsors in
four slots: an overview banner, a rotating sidebar card (max three), the
login page and a new Sponsors page that also lists open placements.

An entry shows only while enable is not false and until is in the
future; links must be https and logos are png/webp/jpg by name only.
The list is cached for an hour and the last good copy survives upstream
failures; logos are proxied through /sponsors/logo/:name with failures
cached, so CSP stays 'self' and admin browsers never reach a third
party. Admins can hide a slot for 24h. Under XUI_DEBUG the panel reads
a sibling ../sponsors/3X checkout so edits can be previewed before push.

internal/web/translation/es-ES.json

@@ -120,6 +120,7 @@
     "outbounds": "Salidas",
     "apiDocs": "Documentación de la API",
     "donate": "Donar",
+    "sponsors": "Patrocinadores",
     "hosts": "Hosts",
     "docs": "Documentación",
     "openMenu": "Abrir menú",
@@ -2256,6 +2257,27 @@
         "badTag": "Etiqueta no válida",
         "badVlessRoute": "Introduce un único número entre 0 y 65535"
       }
+    },
+    "sponsors": {
+      "title": "Patrocinadores",
+      "intro": "Empresas que apoyan el desarrollo de 3X-UI. Los enlaces patrocinados se abren en una pestaña nueva.",
+      "become": "Hazte patrocinador",
+      "tag": "Patrocinador",
+      "visit": "Visitar",
+      "yourBrand": "Tu marca aquí",
+      "yourBrandText": "Muestra tu empresa a miles de administradores de servidores que abren 3X-UI cada día.",
+      "placements": "Espacios disponibles",
+      "placementDashboard": "Banner del panel",
+      "placementDashboardDesc": "Espacio premium en la parte superior del panel, un patrocinador a la vez.",
+      "placementSidebar": "Tarjeta lateral",
+      "placementSidebarDesc": "Se muestra en todas las páginas del panel, rotando entre patrocinadores.",
+      "placementLogin": "Página de inicio de sesión",
+      "placementLoginDesc": "La ve el administrador en cada inicio de sesión.",
+      "placementPage": "Página de patrocinadores",
+      "placementPageDesc": "Aparece aquí con logo, descripción y enlace.",
+      "available": "Disponible",
+      "takenUntil": "Ocupado hasta {date}",
+      "activeCount": "{count} activos"
     }
   },
   "tgbot": {