feat: configure SMTP email notifications across all services

Added comprehensive email configuration to enable notifications for
password resets, user invitations, system alerts, and backup failures.

**Services configured:**

- **Vaultwarden** (vault/compose.yaml):
  - SMTP settings for password resets, 2FA, emergency access emails
  - Uses IONOS SMTP with force_tls security
  - Sender: hi@pivoine.art

- **Linkwarden** (links/compose.yaml):
  - Email server configuration for user invitations
  - Password reset functionality via email
  - Uses smtp:// connection string format

- **n8n** (n8n/compose.yaml):
  - SMTP mode enabled for workflow notifications
  - User invitation emails
  - Password reset support
  - SSL-secured connection

- **Netdata** (netdata/compose.yaml, health_alarm_notify.conf, msmtprc):
  - Health alarm notifications via email
  - MSMTP configuration for sending alerts
  - Notifications sent to valknar@pivoine.art
  - Alerts for system issues, resource exhaustion, service failures

**Common SMTP settings** (from .env):
- Provider: IONOS (smtp.ionos.de:465)
- From address: hi@pivoine.art
- Transport: SMTP with TLS/SSL
- Admin email: valknar@pivoine.art

**Backrest notifications:**
- Configured via web UI at restic.pivoine.art
- Supports webhooks to Gotify for push notifications
- Email notifications can be added through UI settings

All services now have proper email notification capabilities for
improved monitoring, user management, and security features.

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

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

vault/compose.yaml

@@ -12,6 +12,13 @@ services:
       SIGNUPS_ALLOWED: ${VAULT_SIGNUPS_ALLOWED:-false}
       INVITATIONS_ALLOWED: ${VAULT_INVITATIONS_ALLOWED:-true}
       SHOW_PASSWORD_HINT: ${VAULT_SHOW_PASSWORD_HINT:-false}
+      SMTP_HOST: ${EMAIL_SMTP_HOST}
+      SMTP_FROM: ${EMAIL_FROM}
+      SMTP_FROM_NAME: Vaultwarden
+      SMTP_SECURITY: force_tls
+      SMTP_PORT: ${EMAIL_SMTP_PORT}
+      SMTP_USERNAME: ${EMAIL_SMTP_USER}
+      SMTP_PASSWORD: ${EMAIL_SMTP_PASSWORD}
     networks:
       - compose_network
     labels: