fix: add init:true to docker-compose for Node signal handling

Node.js as PID 1 in Docker doesn't handle signals properly,
causing intermittent clean exits (exit code 0) under the
traefik-public network. Using tini via init:true fixes this.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -2,6 +2,7 @@ services:
   xhivart-mirror:
     build: .
     container_name: xhivart-mirror
+    init: true
     restart: always
     environment:
       - SMTP_HOST=${SMTP_HOST}