systemd hands a unit's credentials to every process of that unit, and a
host job is a process of the runner daemon, so the `LoadCredential=` on
gitea-runner-swarm still let any workflow read the registration token
from `$CREDENTIALS_DIRECTORY`.
swarm-ci-runner-register.service, a oneshot under the daemon's dynamic
user and state dir, now holds the only `LoadCredential=` and runs the
precond and `act_runner register` (only when `.runner` is missing). The
daemon unit has no credential, no `EnvironmentFile` and no `TOKEN`; its
pre-start step starts the register unit, so a missing token fails the
daemon's start and `Restart=on-failure` retries it.
The precond compares `.runner`'s labels in the form the daemon rewrites
them to (`nix` -> `nix:host`); compared verbatim, a scheme-less label
re-registered the runner on every start.
tmpfiles removes the unused `registration-token.env` and upstream's
`.token-hash`/`.labels` markers.
8ffceea8e3