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/Caddyfile

@@ -8,6 +8,12 @@
 # Let's Encrypt certificate by itself, and `http://localhost` for the local rehearsal.
 # {$ACCOUNT_SITE} is the account domain handles are on where it isn't {$LEARN_DOMAIN}
 # (`halkyon.eu`), whose profile pages this instance serves; empty for none.
+# Global options an instance's setting adds (compose.forwarded.yaml: behind another
+# server's HAProxy, ADR 0039); none without.
+{
+	import global/*.caddy
+}
+
 {$LEARN_DOMAIN} {$ACCOUNT_SITE} {
 	encode zstd gzip