gitea-runner registration (hive-ci-prefetch, host-side) sits on the
boot-critical path -- nspawn readiness is gated on the runner
registering, itself a forge + core-token round trip that can wait up
to 60s for the core token. The default ~60s TimeoutStartSec can trip
mid-register (especially right after a .runner purge, since every
boot re-registers from scratch), killing the half-started container
and triggering a restart loop until the token/forge settle. Bump to
180s so one register attempt has room to finish.
