docs(admin): add Data-drive encryption (LUKS) article

Covers the opt-in LUKS2 encryption of /docker available on new server
installs. Reboot UX (web unlock at :8444, SSH fallback), threat model
in plain English, what LUKS does and doesn't protect against, header
backup handling, passphrase rotation outline, and the "do not enable
this if you need unattended reboots" caveat.

Sidebar order 7 (after Backups in the admin section).
Linked from the admin overview "What's in this section" list and from
the VDS comparison section of "What is containerized hosting?".

No cost / pricing language by design — operational positioning is
still being decided.

src/content/docs/whp/getting-started/what-is-containerized-hosting.mdx

@@ -41,7 +41,10 @@ A [Virtual Dedicated Server](https://anhonesthost.com/vds) is our VPS-class prod
 
 A VDS suits you when you want full admin control of the server — kernel-level tweaks, custom services, your own systemd units, or you simply prefer to manage the OS yourself. You get a real virtual machine with root access, and WHP still gives you the friendly panel on top.
 
+A VDS also opens up server-wide options that don't apply to shared containers, like opt-in [data-drive encryption](/whp/admin/data-drive-encryption/) for compliance or peace-of-mind scenarios.
+
 ## Related
 
 - [Add-ons overview](/whp/add-ons/overview/)
 - [Service hostnames](/whp/reference/service-hostnames/)
+- [Data-drive encryption (LUKS)](/whp/admin/data-drive-encryption/) — optional, new-server-only