English docs and passwordless SSH mesh for lab fleet

- Translate all documentation to English
- Add docs/ssh-mesh.md and scripts/setup/setup-ssh-mesh.sh
- Add config/hosts/atc-lab.hosts for /etc/hosts on all VMs
- Ignore atc_cluster private key in git; mesh deployed on 12 hosts

scripts/atclab/README.md

@@ -1,12 +1,12 @@
-# atclab scripts (referentie)
+# atclab scripts (reference)
 
-Kopie van `/opt/atclab/bin/` op lab hosts — handige wrappers voor yum/git/syslog.
+Copy of `/opt/atclab/bin/` from lab hosts — yum/git/syslog helpers.
 
-| Script | Functie |
+| Script | Purpose |
 |--------|---------|
-| `atclab-update` | yum update van atclab repo |
+| `atclab-update` | yum update from atclab repo |
 | `gitcommit` | `git commit -m "$@"` shortcut |
 | `gittag` | git tagging helper |
 | `syslog` / `syslogf` | syslog viewers |
 
-Deze scripts zijn host-specifiek; pas aan per omgeving.
+Host-specific; adjust per environment.