Foro (escritura): crear tema y responder, con saneado HTML

- lib/forum-sanitize.ts: cleanPostHtml con sanitize-html (misma allowlist que
  forum/sanitize.py de nh3: formato básico + a/img/tablas, rel nofollow, esquemas
  http/https/mailto). Verificado XSS-safe (script/onclick/javascript: eliminados).
- lib/forum-write.ts: createTopic (tema + primer post), createPost (respuesta +
  updated_at), forumIsPostable / topicIsReplyable.
- Routes /api/forum/topic y /api/forum/reply (guard de sesión; identidad = cuenta de
  juego: poster=username, poster_id=accountId). Componentes NewTopicForm y ReplyForm
  (clientes). Se muestran solo si hay sesión; el tema cerrado no admite respuesta.

Verificado: escritura 401 sin sesión, saneado correcto. Pendiente: editar/borrar,
moderación (fijar/cerrar/mover), búsqueda, editor enriquecido.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-next/messages/en.json

@@ -254,6 +254,16 @@
     "backToTopics": "Back to forum",
     "notFound": "Not found",
     "newTopic": "New topic",
-    "reply": "Reply"
+    "reply": "Reply",
+    "newTopicName": "Topic title",
+    "newTopicText": "Write your message…",
+    "publish": "Post topic",
+    "publishing": "Posting…",
+    "replyText": "Write your reply…",
+    "sendReply": "Reply",
+    "sending": "Sending…",
+    "loginToPost": "Sign in to participate.",
+    "emptyError": "Fill in all fields.",
+    "genericError": "Something went wrong. Please try again later."
   }
 }

web-next/messages/es.json

@@ -254,6 +254,16 @@
     "backToTopics": "Volver al foro",
     "notFound": "No encontrado",
     "newTopic": "Nuevo tema",
-    "reply": "Responder"
+    "reply": "Responder",
+    "newTopicName": "Título del tema",
+    "newTopicText": "Escribe tu mensaje…",
+    "publish": "Publicar tema",
+    "publishing": "Publicando…",
+    "replyText": "Escribe tu respuesta…",
+    "sendReply": "Responder",
+    "sending": "Enviando…",
+    "loginToPost": "Inicia sesión para participar.",
+    "emptyError": "Completa todos los campos.",
+    "genericError": "Algo ha salido mal. Inténtalo más tarde."
   }
 }