[RESILIENCE] Automatic backup scheduling — periodic snapshots with configurable retention

[ElioNeto]

Description

ApexStore has manual snapshot capability but no automatic scheduled backups. Production deployments need automated backups.

Implementation

1. Add BackupScheduler background thread
2. Configuration:

resilience:
  backup:
    enabled: true
    interval_secs: 3600  # hourly
    retention_days: 30
    directory: /var/backups/apexstore
    compress: true
    upload_to_s3: false  # optional S3 upload
    s3_bucket: ""
    s3_prefix: "backups/"

3. Backup naming: snap-{cf}-{timestamp}
4. Retention policy: delete backups older than N days
5. Alert on backup failure (via webhook)
6. List scheduled backups: GET /admin/backups

Labels

[ElioNeto]

Implemented in commit 0871d91.