The TOML dependency is added to `Cargo.lock` to support configuration
file parsing.
New modules `config` and `startup` are introduced in
`doctate-client-core`:
- `config`: Handles client configuration loading and saving, including
defaults for polling intervals and window hours.
- `startup`: Contains routines for initial cleanup tasks, such as
removing stale markers and orphan audio files based on defined
retention periods.
Brummel