Add Support for Exporting Transcription Results to Subtitle Formats (VTT, SRT, etc.)

Currently, the app transcribes audio/video files into plain text only. It would be useful to allow exporting transcripts as subtitle files such as .vtt, .srt, or other common formats.

Benefits:

• Use transcripts directly in video editing

• Save time by avoiding manual timestamp formatting

• Improve accessibility and multilingual workflows

Suggested Behavior:

• After transcription, allow download as .txt, .vtt, or .srt

• Optionally, enable subtitle customization (line length, line break rules, timestamp format)

So adding subtitle export will integrate well with existing capabilities.