mavend: say the act replies from the file (V-504)

Also fixes a flake this stack introduced: the feeds test matched "ничего
нового" as a substring, and query_ru_v1.json can answer with "в лентах тихо".
It asks the entry now, like the others.

cmd/mavend/feeds_test.go

@@ -94,7 +94,7 @@ func TestQueryFeedsOffAndEmptyDiffer(t *testing.T) {
 	}
 	on := buildFeedHandler(t, true)
 	reply, ok = askFeeds(t, on, "что нового в лентах?")
-	if !ok || !strings.Contains(reply, "ничего нового") {
+	if !ok || !phraser.IsQ(phraser.QueryFeedsEmpty, nil, reply) {
 		t.Fatalf("feeds on but empty: reply = %q, ok = %v", reply, ok)
 	}
 }