Slurm's shared files and users: one path everywhere, accounts as Linux users

slurm.shared mounts the site's NFS export, has an llmgw node export the path
over NFS to the Slurm machines alone (2049 in the firewall), or looks for a
file system the site mounts. slurm.users "llmgw" makes each active account a
Linux user on every Slurm machine: login from its e-mail, a UID from 200000
kept in slurm_users and never reused, its home on the shared path, its SSH
keys from the portal's Profile (or ctl slurm users keys) read by sshd from
/etc/llmgw/ssh-keys. server init --slurm chooses /shared from the first
machine and llmgw's users; --slurm-shared and --slurm-users change that.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/control/adminapi/api.go

@@ -98,6 +98,8 @@ type API struct {
 	usage     Usage
 	quotas    Quotas
 	ctl       *control.Controller
+	// slurmUsers are the Linux users made from the accounts; nil without a store.
+	slurmUsers SlurmUsers
 }
 
 // New builds the API over a controller.