fix xlab-gateway host key in secrets.nix and rekey ...

The active host key on xlab-gateway is the original one
(AAAAII+EKDpU...), not the replacement. Corrected and rekeyed.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

add ylw ed25519 key: agenix access, SSH auth, rekey all secrets ...

- Add ylw's ed25519 public key to secrets.nix admins list
- Re-encrypt all .age secrets so ylw can decrypt
- Add ed25519 key to ye-lw21 authorized SSH keys

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

skydick: switch Samba to ldapsam, rename ylw→ye-lw21, drop legacy datasets ...

- Samba passdb backend changed from tdbsam to ldapsam:ldap://10.0.0.1
- Added samba-ldap-admin-password oneshot to seed LDAP admin cred before smbd
- Pinned storage group to GID 997 to match LDAP posixGroup
- Renamed ylw to ye-lw21 across all hosts (users.nix, skydick, xlab-gateway)
- Removed legacy tmpfiles and NFS exports (share/backup/torrent/vm destroyed)
- Added bootstrap LDIF for sambaDomain, storage group, machines OU

Co-Authored-By: Claude Opus 4.6 <[email protected]>