feat: add Restic backup stack with Backrest UI

Added comprehensive backup solution to The Falcon infrastructure:

- **Restic Stack** (restic.pivoine.art):
  - Backrest web UI for managing restic backups
  - Automated scheduled backups with retention policies
  - Real-time backup status and monitoring
  - Restore capabilities via web interface

- **Backup Configuration**:
  - Target: /mnt/hidrive/users/valknar/Backup
  - Backs up all critical Docker volumes read-only:
    - PostgreSQL, Redis, Directus (uploads/bundle)
    - Awesome, Gotify, Scrapy (data/code)
    - n8n workflows, Filestash state
    - Linkwarden bookmarks/search index
    - Let's Encrypt SSL certificates

- **Infrastructure Updates**:
  - Added RESTIC_* environment variables to arty.yml
  - Updated compose.yaml to include restic stack
  - Updated README.md and CLAUDE.md documentation
  - Configured Traefik routing with SSL

All volumes mounted read-only to backup container for safety.
Backrest data persisted across: data, config, cache, tmp volumes.

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

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

arty.yml

@@ -87,6 +87,13 @@ envs:
     LINKS_DB_NAME: linkwarden
     LINKS_MEILI_IMAGE: getmeili/meilisearch:v1.12.8
     LINKS_MEILI_NO_ANALYTICS: true
+    # Restic
+    RESTIC_TRAEFIK_ENABLED: true
+    RESTIC_COMPOSE_PROJECT_NAME: restic
+    RESTIC_IMAGE: garethgeorge/backrest:latest
+    RESTIC_TRAEFIK_HOST: restic.pivoine.art
+    RESTIC_HOSTNAME: falcon
+    RESTIC_BACKUP_PATH: /mnt/hidrive/users/valknar/Backup
     # Proxy
     PROXY_COMPOSE_PROJECT_NAME: proxy
     PROXY_DOCKER_IMAGE: traefik:latest