Foro (lectura): índice, temas y mensajes en Next.js

- lib/forum.ts: getForumIndex (categorías + foros visibles con contadores y último
  tema, port de forum/db.py), getForum/getTopics, getTopic/getPosts (acore_web).
- Páginas app/[locale]/forum (índice), /forum/[forumId] (temas), /forum/topic/[topicId]
  (mensajes; render del HTML ya saneado por Django). Enlace "Foros" en la cabecera.
- Catálogo Forum + Nav.forum.

Verificado: /forum 200, foros/temas inexistentes 404, enlace en la cabecera.
Solo lectura; pendiente escribir (crear tema/responder + saneado nh3->TS) y moderación.

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

web-next/messages/en.json

@@ -9,7 +9,8 @@
     "register": "Create account",
     "account": "My account",
     "logout": "Log out",
-    "language": "Language"
+    "language": "Language",
+    "forum": "Forums"
   },
   "Home": {
     "brand": "Nova WoW",
@@ -237,5 +238,22 @@
     "success": "Email changed successfully! You can now sign in with the new email.",
     "error": "The link is invalid, expired or the account was not found.",
     "goLogin": "Go to sign in"
+  },
+  "Forum": {
+    "title": "Forums",
+    "noForums": "No forums available yet.",
+    "topics": "Topics",
+    "posts": "Posts",
+    "lastTopic": "Latest topic",
+    "by": "by",
+    "views": "Views",
+    "noTopics": "No topics in this forum yet.",
+    "locked": "Locked",
+    "sticky": "Pinned",
+    "backToForum": "Back to forums",
+    "backToTopics": "Back to forum",
+    "notFound": "Not found",
+    "newTopic": "New topic",
+    "reply": "Reply"
   }
 }