Integrate local transcription service and save transcript to disk

[olpa]

Goal

An uploaded audio file is automatically transcribed and the transcript is saved alongside it.

Tasks

• After saving audio.webm, call the local transcription service:
  POST http://localhost:9000/transcribe
• Pass the audio file; receive { "text": "..." } in response
• Write the transcript to data/note-<id>/transcript.txt
• Handle transcription errors gracefully (log and continue; don't fail the upload)

Done when

After recording and uploading, transcript.txt appears in the note directory with the spoken text.