fix(uptime-kuma): add proxy network for internet access to Discord/Telegram

Container was on backend (internal: true) only — couldn't resolve
discord.com for webhook notifications. Added proxy network which
has outbound internet access.

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

roles/services/templates/docker-compose.yml.j2

@@ -573,6 +573,7 @@ services:
       - no-new-privileges:true
     networks:
       - backend
+      - proxy  # needs internet access for Discord/Telegram notifications
     volumes:
       - uptime_kuma_data:/app/data
     healthcheck: