docs(deploy): the unlock at boot from melchior's ssh config, the address the FRITZ!Box keeps

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

deploy/host/README.md

@@ -90,8 +90,24 @@ for the later.
    ```
 
    The last line is dropbear's own host key, which melchior sees on port 2222 at the
-   next boot. At that boot, at home: `ssh -p 2222 root@192.168.178.53` from melchior asks
-   for the root disk's passphrase, and the boot goes on. The keyboard at the iMac still
+   next boot. melchior's key isn't at one of ssh's default paths, so it is named for the
+   unlock in melchior's `~/.ssh/config`, its host key apart from sshd's:
+
+   ```
+   Host balthasar-unlock
+       HostName 192.168.178.53
+       Port 2222
+       User root
+       IdentityFile ~/.ssh/raisondetredev@ramiel
+       IdentitiesOnly yes
+       HostKeyAlias balthasar-unlock
+   ```
+
+   At the next boot, at home: `ssh balthasar-unlock` from melchior asks for the root
+   disk's passphrase, and the boot goes on. Both the boot image and the system ask the
+   FRITZ!Box for their address, differently (the system with a client ID), so the
+   FRITZ!Box keeps 192.168.178.53 for balthasar's MAC address, `00:50:B6:BF:FC:FF`
+   (step 1); without it, the system got another address than the boot image. The keyboard at the iMac still
    works as before. Should the new image not open the disk, choose *the way back* in
    GRUB's menu at the iMac: it boots as before this step. Once the new images have
    booted: `sudo rm /etc/grub.d/41_dracut_fallback /boot/initrd.img-*.dracut && sudo update-grub`.