Cierra el flujo de login: logout, selector de cuenta y /account con guardas

- Route handlers: /api/auth/logout (destroy sesión), /api/auth/select-account
  (fija la cuenta de juego elegida, valida que pertenece a la bnet en sesión).
- app/[locale]/select-account: página SSR (guarda: sin bnetId -> login) + lista de
  cuentas de juego (SelectAccountForm cliente) -> /account.
- app/[locale]/account: página protegida (sin bnetId -> login; sin username ->
  select-account) con datos de sesión + LogoutButton.
- Textos en messages (Account, SelectAccount).

Verificado: guardas locale-aware (ES /account -> /login, EN /en/account -> /en/login,
307), logout OK, select-account sin sesión 401. Redirect i18n con next-intl.

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

web-next/messages/en.json

@@ -30,5 +30,19 @@
     "forgot": "I forgot my password/username",
     "newHere": "New to the community? You can create an account",
     "createAccount": "here"
+  },
+  "Account": {
+    "title": "My account",
+    "bnetAccount": "Account (Battle.net)",
+    "gameAccount": "Game account",
+    "logout": "Log out"
+  },
+  "SelectAccount": {
+    "title": "Select your game account",
+    "loggedInAs": "Logged in as",
+    "choose": "Your Battle.net account has several game accounts. Choose which one to continue with:",
+    "noAccounts": "No game accounts were found linked to this Battle.net account.",
+    "entering": "Entering…",
+    "error": "The account could not be selected."
   }
 }