Let a downloaded program be downloaded again

The button disappeared the moment anything landed, and nothing else on
the window asks for that download. So a machine that got the processor
build before its graphics driver was installed can never be given the
Vulkan one, and nobody can pick up a newer whisper.cpp either: both of
those are the same missing control.

It reads "Download again" once a copy is here, and stays hidden while a
system one is on the PATH, because that is the copy that would run.

dikte/i18n.py

@@ -779,6 +779,7 @@ TR = {
     "Local model": "Yerel model",
     "Not installed.": "Kurulu değil.",
     "Installed on the system: {path}": "Sistemde kurulu: {path}",
+    "Download again": "Yeniden indir",
     "Downloaded, version {version}.": "İndirildi, sürüm {version}.",
     "Downloaded, version {version}. There was no Vulkan build, "
     "so this one runs on the processor.":