feat(services): HTTP/2 + HTTP/3 support via Caddy reverse-proxy

Swap Werkzeug for Caddy as the protocol layer for http and https decoy
services. Flask keeps owning app logic (fake_app, custom_body, headers,
syslog) on 127.0.0.1:8080; Caddy terminates h1/h2/h2c/h3 on the wire
with real-world TLS/QUIC fingerprints.

- Add `multi_enum` FieldType to ServiceConfigField + _coerce
- Add `http_versions` field to HTTPService (h1/h2c) and HTTPSService
  (h1/h2/h3); selecting h3 emits UDP/443 port mapping in compose
- Rewrite both Dockerfiles with multi-stage Caddy binary copy +
  setcap for port binding as the logrelay user
- Entrypoints parse HTTP_VERSIONS JSON, render a Caddyfile, start
  Flask in background, wait for it, then exec Caddy
- https/server.py drops direct TLS handling; Caddy owns the cert
- Add ProxyFix to both server.py so Flask sees real attacker IPs
- Frontend: multi_enum checkbox-group renderer in ServiceConfigFields;
  FormValue union extended to string[]; compactPayload skips []
- Fix stale test_smtp_relay_schema_matches_smtp: relay schema is a
  superset of smtp, not equal; update assertions accordingly

decnet/templates/https/Dockerfile

@@ -1,6 +1,10 @@
+FROM caddy:2 AS caddy-bin
+
 ARG BASE_IMAGE=debian:bookworm-slim@sha256:f9c6a2fd2ddbc23e336b6257a5245e31f996953ef06cd13a59fa0a1df2d5c252
 FROM ${BASE_IMAGE}
 
+COPY --from=caddy-bin /usr/bin/caddy /usr/bin/caddy
+
 RUN apt-get update && apt-get install -y --no-install-recommends \
     python3 python3-pip openssl \
     && rm -rf /var/lib/apt/lists/*
@@ -17,12 +21,18 @@ RUN chmod +x /entrypoint.sh
 RUN mkdir -p /opt/tls
 
 EXPOSE 443
+
 RUN useradd -r -s /bin/false -d /opt logrelay \
  && chown -R logrelay:logrelay /opt/tls \
+ && mkdir -p /etc/caddy /opt/.local/share/caddy /opt/.config/caddy \
+ && chown -R logrelay:logrelay /etc/caddy /opt/.local /opt/.config \
  && apt-get update && apt-get install -y --no-install-recommends libcap2-bin \
  && rm -rf /var/lib/apt/lists/* \
+ && setcap 'cap_net_bind_service+eip' /usr/bin/caddy \
  && (find /usr/bin/ -maxdepth 1 -name 'python3*' -type f -exec setcap 'cap_net_bind_service+eip' {} \; 2>/dev/null || true)
 
+ENV XDG_DATA_HOME=/opt/.local/share XDG_CONFIG_HOME=/opt/.config
+
 HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
   CMD kill -0 1 || exit 1