feat(deploy): halkyon.li's forward through ramiel and its host at home (ADR 0039)

ramiel's HAProxy passes halkyon.li's TLS connections, unopened, through a
WireGuard tunnel to the instance at home, with the visitor's address in a
PROXY header, and everything else to ramiel's own Caddy, moved to the
loopback. Each end's nftables table lets the tunnel carry HAProxy's 443 and
the SSH jump's 22 alone, and nothing from home to ramiel.

The host at home: sshd with keys alone, the root disk unlocked over SSH at
boot (dropbear-initramfs, D20), Docker's and containerd's data bind-mounted
from the HDD, and home's end of the tunnel before Docker. An instance behind
the forward (compose.forwarded.yaml) publishes 443 on the tunnel's address
alone, trusts the PROXY header from ramiel alone, and gets its certificates
through TLS-ALPN, without HTTP/3.

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/dropbear.conf

@@ -0,0 +1,11 @@
+# The SSH server of the initramfs, through which the root disk's passphrase is typed at
+# boot (ADR 0039, D20), as /etc/dropbear/initramfs/dropbear.conf on the instance's host
+# at home. It waits on the home network alone (the tunnel to ramiel isn't up that
+# early), on 2222, so its host key never clashes with sshd's in melchior's known_hosts.
+#
+#   -p 2222              its port
+#   -s                   no passwords: melchior's key alone
+#   -j -k                no forwarding of any kind
+#   -I 300               a connection idle for 5 minutes is closed
+#   -c cryptroot-unlock  runs nothing but the unlock, whatever the client asks
+DROPBEAR_OPTIONS="-p 2222 -s -j -k -I 300 -c cryptroot-unlock"