feat: the assistant's search engine in Настройки - DuckDuckGo, a SearXNG of one's own, Brave Search or Tavily, with DuckDuckGo behind the chosen one

internal/server/web/static/app.css

@@ -1025,3 +1025,7 @@ body.no-motion *, body.no-motion *::before, body.no-motion *::after, body.no-mot
 .fp-ring circle { fill:none; stroke-width:2.6; }
 .fp-ring .bg { stroke:var(--border); }
 .fp-ring .fg { stroke:var(--accent); stroke-linecap:round; stroke-dasharray:100; stroke-dashoffset:calc(100 - var(--up, 0)); transition:stroke-dashoffset .25s ease; }
+/* Настройки › ИИ-ассистент › поиск: the fields of the engine chosen. */
+.ai-form .ai-sub { margin:10px 0 0; font-size:15px; }
+.ai-form:not([data-search="searxng"]) .s-url { display:none; }
+.ai-form:not([data-search="brave"]):not([data-search="tavily"]) .s-key { display:none; }