feat: add Jellyfin config backup to Restic

Added jellyfin-backup plan to Backrest configuration:
- Backs up /volumes/jelly_config daily at 9 AM
- Retention: 7 daily, 4 weekly, 6 monthly, 2 yearly
- Added jelly_config volume mount to restic/compose.yaml
- Updated documentation in CLAUDE.md

This ensures Jellyfin configuration, library metadata, and user
settings are backed up to HiDrive.

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

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

restic/config.json

@@ -226,6 +226,22 @@
           "yearly": 2
         }
       }
+    },
+    {
+      "id": "jellyfin-backup",
+      "repo": "hidrive-backup",
+      "paths": ["/volumes/jelly_config"],
+      "schedule": {
+        "cron": "0 9 * * *"
+      },
+      "retention": {
+        "policyTimeBucketed": {
+          "daily": 7,
+          "weekly": 4,
+          "monthly": 6,
+          "yearly": 2
+        }
+      }
     }
   ]
 }