Replace Pebble with step-ca for local ACME

Pebble skipped real HTTP-01 validation, which hid integration gaps
for compliance-page custom domains. step-ca with a Caddy port-80
proxy exercises the same path production uses while keeping issued
certs persistent across compose restarts.

Signed-off-by: Bryan Frimin <bryan@probo.com>

compose/caddy/Caddyfile

@@ -0,0 +1,5 @@
+# Proxies ACME HTTP-01 validation (port 80) to probod's trust-center HTTP
+# listener on the host (:10080 by default).
+:80 {
+	reverse_proxy host.docker.internal:10080
+}