feat(deploy): Jellyfin at home, published through WireGuard (ADR 0032)

The instance serves jellyfin.halkyon.eu and its Caddy proxies through a
WireGuard tunnel to a Jellyfin on the operator's own machine, which dials
out, so nothing names the home network's address and its router opens no
port. compose.jellyfin-home.yaml takes the sidecar's place, with its
site's rules unchanged (jellyfin.caddy's upstream is now a setting), and
leaves JELLYFIN_URL unset, so the instance suggests it only while it
answers.

On the instance's server the tunnel reaches Jellyfin from Caddy alone and
nothing of the host (wg-jellyfin-rules.sh, set and removed with the
tunnel); the CI runner's unit denies it, and CI's Sandbox step fails if a
job reaches it. The home end keeps Jellyfin in WireGuard's network
namespace, its port on the loopback alone. The steps are in
deploy/sidecars/README.md, the rules held by test/deploy/jellyfin_home_test.dart.

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/compose.jellyfin-home.yaml

@@ -0,0 +1,27 @@
+# Jellyfin at home, published by the instance (ADR 0032): the Jellyfin sidecar's site,
+# with Caddy proxying through a WireGuard tunnel to a Jellyfin on the operator's own
+# machine (home-jellyfin/), rather than to one beside the instance. Nothing of the home
+# network shows: people reach the instance's server alone. Switched on in .env, in place
+# of compose.jellyfin.yaml, never beside it:
+#
+#   COMPOSE_FILE=compose.yaml:compose.jellyfin-home.yaml
+#   JELLYFIN_DOMAIN=jellyfin.halkyon.eu
+#
+# The tunnel is the host's (wg-quick@wg-jellyfin, with the rules letting Caddy alone
+# through it), set up once as root: sidecars/README.md, *Jellyfin at home*.
+
+services:
+  caddy:
+    environment:
+      JELLYFIN_DOMAIN: ${JELLYFIN_DOMAIN:?set JELLYFIN_DOMAIN in deploy/.env}
+      # The home end's address in the tunnel (D3).
+      JELLYFIN_UPSTREAM: 10.61.96.2:8096
+    volumes:
+      - ./sidecars/jellyfin.caddy:/etc/caddy/sidecars/jellyfin.caddy:ro
+
+  server:
+    # No JELLYFIN_URL (D9): the instance looks at jellyfin. on its own domain and
+    # suggests it only while it answers, as the home end is away whenever its machine
+    # is. It looks through Caddy on edge, not by the public address back in.
+    extra_hosts:
+      - ${JELLYFIN_DOMAIN:?set JELLYFIN_DOMAIN in deploy/.env}:172.30.80.2