Save the transcript as subtitles too, not just as text

whisper-1's verbose response carries a start and an end for every segment,
and the file tab was reading only the start, to build the [mm:ss] prefix.
Keeping the end as well is all an SRT needs.

The text stays the authority on wording and the segments on timing; they
meet at that prefix, which the cleanup model is already told to leave alone.
So a transcript that went through cleanup still turns into properly timed
subtitles. A line whose stamp matches no segment runs until the next line
starts, a line with no stamp at all joins the cue above it, and an end that
would run into the next cue is trimmed back.

The button is dead until a timestamped run finishes, because without
timestamps there are no segments to time anything with.

README.tr.md

@@ -81,7 +81,7 @@ süreyi, ardından hangi aşamada olduğunu gösterir. Odak almaz. Dikte çalı
   normal bir çalışma gibi görünmez.
 - **Ses ve video dosyaları** Ayarlar → Ses dosyası sekmesinde aynı modellerden
   geçer; istersen `[dd:ss]` zaman damgalarıyla, uzun dosyalar ffmpeg ile
-  parçalanarak.
+  parçalanarak, sonuç `.txt` ya da `.srt` altyazı olarak kaydedilerek.
 - **Geçmiş** Ayarlar → Geçmiş sekmesinde; boyut sınırı var, sağ tıklayıp
   silebilirsin.
 - **Türkçe ve İngilizce arayüz**, varsayılan olarak sistem dilini izler.