feat: several models for the assistant, each with its own name, kind, address and key; a model menu in the chat when there are several (or always, from Аккаунт › Вид), the choice kept for the user

internal/server/web/static/prefs.js

@@ -5,6 +5,8 @@
   let p = Object.assign({}, (window.APP && window.APP.prefs) || {});
   function apply() {
     const b = document.body;
+    // Parts that follow a setting of their own (the chat's model menu).
+    document.dispatchEvent(new CustomEvent('lpra:prefs'));
     b.dataset.tabicons = p.tabIcons || 'left';
     b.classList.toggle('compact', !!p.compact);
     b.classList.toggle('no-ftime', p.fileTime === 'hide');