Add X-Forwarded-Proto header middleware to OnlyOffice template

Fixes mixed content errors when OO is behind Traefik HTTPS reverse
proxy. Without this, OO Document Server generates http:// URLs for
editor resources, which browsers block on HTTPS pages.

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

templates/onlyoffice/docker-compose.yml

@@ -36,6 +36,8 @@ services:
       - "traefik.http.routers.onlyoffice.entrypoints=websecure"
       - "traefik.http.routers.onlyoffice.tls=true"
       - "traefik.http.routers.onlyoffice.tls.certresolver=letsencrypt"
+      - "traefik.http.routers.onlyoffice.middlewares=onlyoffice-headers"
+      - "traefik.http.middlewares.onlyoffice-headers.headers.customrequestheaders.X-Forwarded-Proto=https"
       - "traefik.http.services.onlyoffice.loadbalancer.server.port=80"
 
 volumes: