- Config: max_backups_per_file (default 10) in config.json + UI field
- Auto-cleanup: _backup_file deletes oldest backups when limit exceeded
- New endpoints: GET /api/backups (list all), POST /api/backups/delete,
POST /api/backups/purge (by file or vault)
- New module: backup-manager.js - full-page view with filter, grouped by
vault/file, individual delete, per-file purge, stats
- Link from backup viewer footer: 'Gerer tous les backups'
