Launch and deploy a new application to Fly.io with flyctl

Documented steps

1. Install flyctl (brew install flyctl on macOS, or curl -L https://fly.io/install.sh | sh) and log in: fly auth login.
2. From your project's source directory run `fly launch`. It scans the code, detects a Dockerfile, buildpacks, or a supported framework, creates an app and a fly.toml, and asks whether to deploy immediately.
3. To configure env/secrets/volumes before the first deploy (or to just scaffold), use `fly launch --no-deploy`, then edit fly.toml and deploy later with `fly deploy`.
4. fly launch sets the app name (derived from the directory unless you choose one), the region (fastest for you, becomes primary_region), and a default VM size (e.g. shared-cpu-1x / 1GB). internal_port in fly.toml is taken from the Dockerfile's EXPOSE, defaulting to 8080 if none is found.
5. Deploy/redeploy with `fly deploy`; by default it uses a remote builder to build and push the image, then updates Machines with a rolling strategy.
6. Confirm success with `fly status -a <app>` and open the app with `fly apps open` (or the printed https://<app>.fly.dev URL).
7. Official docs: https://fly.io/docs/launch/ and https://fly.io/docs/getting-started/dockerfile/