feat: update Restic backup configuration

Updated Restic backup system to include all current services:

**Volume Mounts Added:**
- vpn_etc_wireguard (WireGuard VPN configuration)
- netdata_config (Netdata monitoring configuration)

**Backup Plans Updated:**
- Replaced gotify-backup with mattermost-backup
  - Now backs up: mattermost_config, mattermost_data, mattermost_plugins
  - Retention: 7 daily, 4 weekly, 6 monthly, 2 yearly
- Added tandoor-backup
  - Backs up: tandoor_staticfiles, tandoor_mediafiles
  - Schedule: 5 AM daily
  - Retention: 7 daily, 4 weekly, 6 monthly
- Added vpn-backup
  - Backs up: vpn_etc_wireguard (critical for VPN restoration)
  - Schedule: 9 AM daily
  - Retention: 7 daily, 4 weekly, 12 monthly, 3 yearly
- Added netdata-backup
  - Backs up: netdata_config
  - Schedule: 10 AM daily
  - Retention: 7 daily, 4 weekly, 3 monthly

**Backup Schedule:**
- 2 AM: postgres, joplin
- 3 AM: redis
- 4 AM: directus (uploads, bundle)
- 5 AM: awesome, mattermost, tandoor
- 6 AM: scrapy, n8n
- 7 AM: filestash, linkwarden
- 8 AM: letsencrypt, vaultwarden
- 9 AM: jellyfin, vpn
- 10 AM: netdata

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

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

restic/compose.yaml

@@ -35,6 +35,8 @@ services:
       - backup_vaultwarden_data:/volumes/vaultwarden_data:ro
       - backup_joplin_data:/volumes/joplin_data:ro
       - backup_jelly_config:/volumes/jelly_config:ro
+      - backup_vpn_etc_wireguard:/volumes/vpn_etc_wireguard:ro
+      - backup_netdata_config:/volumes/netdata_config:ro
 
     environment:
       TZ: ${TIMEZONE:-Europe/Berlin}
@@ -134,6 +136,12 @@ volumes:
   backup_jelly_config:
     name: jelly_config
     external: true
+  backup_vpn_etc_wireguard:
+    name: vpn_etc_wireguard
+    external: true
+  backup_netdata_config:
+    name: netdata_config
+    external: true
 
 networks:
   compose_network: