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/ai.go

@@ -679,6 +679,14 @@ func (s *Server) handleSetAI(w http.ResponseWriter, r *http.Request) {
 	_ = s.db.SetConfig(cfgAIModel, strings.TrimSpace(r.FormValue("ai_model")))
 	// The field shows the key there; what it holds is the key (empty: none).
 	_ = s.db.SetConfig(cfgAIKey, strings.TrimSpace(r.FormValue("ai_key")))
+	// The search engine for «Поиск».
+	eng := r.FormValue("ai_search")
+	if eng != "searxng" && eng != "brave" && eng != "tavily" {
+		eng = ""
+	}
+	_ = s.db.SetConfig(cfgSearchEngine, eng)
+	_ = s.db.SetConfig(cfgSearchURL, strings.TrimSpace(r.FormValue("ai_search_url")))
+	_ = s.db.SetConfig(cfgSearchKey, strings.TrimSpace(r.FormValue("ai_search_key")))
 	http.Redirect(w, r, "/settings#ai", http.StatusSeeOther)
 }