feat: create net stack consolidating proxy, netdata, watchtower, and umami

- Create net/compose.yaml with 4 services (traefik, netdata, watchtower, umami)
- Update arty.yml with NET_* environment variables
- Update compose.yaml to include net instead of individual stacks
- Update restic volume references to net_letsencrypt_data and net_netdata_config
- Copy configuration files to net/ directory (Dockerfile, dynamic/, go.d/, etc.)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

net/health_alarm_notify.conf

@@ -0,0 +1,47 @@
+# Netdata health alarm notification configuration
+# This file configures where to send alarm notifications
+
+# Enable/disable sending email notifications
+SEND_EMAIL="YES"
+
+# Recipient email address for all alarms
+DEFAULT_RECIPIENT_EMAIL="${ADMIN_EMAIL}"
+
+# Email sender address
+EMAIL_SENDER="${EMAIL_FROM}"
+
+# SMTP configuration
+SENDMAIL=""
+EMAIL_SENDER="${EMAIL_FROM}"
+
+# Custom send email command using msmtp
+EMAIL_COMMAND="msmtp -t"
+
+# Enable specific notification types
+role_recipients_email[sysadmin]="${ADMIN_EMAIL}"
+role_recipients_email[domainadmin]="${ADMIN_EMAIL}"
+role_recipients_email[dba]="${ADMIN_EMAIL}"
+role_recipients_email[webmaster]="${ADMIN_EMAIL}"
+role_recipients_email[proxyadmin]="${ADMIN_EMAIL}"
+role_recipients_email[sitemgr]="${ADMIN_EMAIL}"
+
+###############################################################################
+# Mattermost notifications via Slack-compatible webhook
+###############################################################################
+
+# Enable Slack notifications (Mattermost supports Slack-compatible webhooks)
+SEND_SLACK="YES"
+
+# Mattermost incoming webhook URL (Slack-compatible)
+SLACK_WEBHOOK_URL="${MATTERMOST_WEBHOOK_URL}"
+
+# Slack channel (optional, webhook default channel will be used if empty)
+DEFAULT_RECIPIENT_SLACK=""
+
+# Slack notification recipients per role
+role_recipients_slack[sysadmin]="notifications"
+role_recipients_slack[domainadmin]="notifications"
+role_recipients_slack[dba]="notifications"
+role_recipients_slack[webmaster]="notifications"
+role_recipients_slack[proxyadmin]="notifications"
+role_recipients_slack[sitemgr]="notifications"