Set a fixed width on the caption bubble via `gtk_widget_set_size_request()` using
the effective width parameter, and change label alignment from center to left with
fill halign. Update the `--overlay-max-width` help text and README description to
reflect the new fixed-width behavior (still capped at 80% of monitor width).
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.
Restructure Go source code into a dedicated `src/` directory, rename the project from "audio-listen" to "Captioneer", and update README accordingly. Add `.gitignore` entry for the built binary `captioneer`.
kato