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/frag_test.go

@@ -144,6 +144,14 @@ func TestViewPrefs(t *testing.T) {
 	if got := get(t, s, c, "/api/panel/account/prefs").Body.String(); !strings.Contains(got, `"openHere":"off"`) {
 		t.Fatalf("openHere off not kept: %s", got)
 	}
+	post(`{"aiModelPick":"always","aiModel":"a1b2c3"}`)
+	if got := get(t, s, c, "/api/panel/account/prefs").Body.String(); !strings.Contains(got, `"aiModelPick":"always"`) || !strings.Contains(got, `"aiModel":"a1b2c3"`) {
+		t.Fatalf("the model choice not kept: %s", got)
+	}
+	post(`{"aiModelPick":"often","aiModel":"<x>"}`)
+	if got := get(t, s, c, "/api/panel/account/prefs").Body.String(); strings.Contains(got, "aiModel") {
+		t.Fatalf("an unknown model choice was kept: %s", got)
+	}
 	post(`{"openHere":"sometimes"}`)
 	if got := get(t, s, c, "/api/panel/account/prefs").Body.String(); strings.Contains(got, "openHere") {
 		t.Fatalf("an unknown openHere was kept: %s", got)