hive-ci-register.service now runs unconditionally on every boot (not
just when .runner is absent). Before fetching a registration token it
validates existing .runner credentials via the forge admin API:
- 200: runner still registered, write dummy token and exit
- 404: runner deleted from forge, purge .runner and re-register
- 000: forge unreachable, keep credentials (runner surfaces the error)
- other non-200 or malformed .runner: purge and re-register
Removes ConditionPathExists so stale credentials from a wiped forge
no longer block the runner indefinitely. Updates docs/ci.md to match.
9d816431dc