This commit introduces the capability to configure user-specific Whisper
settings, including language, hotwords, and initial prompts. These
settings are stored in `users.toml` and are passed to the Whisper
service for more tailored transcription results.
New unit tests have been added to verify that the `transcribe` function
correctly forwards these optional settings to the Whisper client and
omits them when they are not provided.
Additionally, a new directory `tests/fixtures/dictations` has been
created to store M4A audio files, their expected transcripts, and
associated hotword files. This serves as a regression corpus for the
Whisper pipeline. A README file explains the structure and conventions
for adding new fixtures. Several new fixtures have been added, covering
various medical domains and transcription scenarios.
