Introduce a supervised child process for capture, VAD, and recognition,
enabling automatic restart on crash/hang and hot-reload via SIGHUP.
Add `--model-auto-restart`, `--model-timeout`, and
`--model-shutdown-timeout` options. Refactor `Run()` with lifecycle
hooks for proper process group cleanup. Update README with new
behavior and CLI flags.
Move the executable entry point to `src/cmd/captioneer` and split audio, capture, config, caption, and model logic into separate packages under `src/`. Update README with new build/run commands and a package-overview section.
kato