feat: configuration backup management with manual and auto backup

Add backup/restore functionality for the SQLite database. Users can
trigger manual backups, configure automatic backups on an interval
with retention policies, list/download/delete backups, and restore
from any backup.

- Backup engine using VACUUM INTO (safe with WAL mode)
- Backup metadata tracked in DB, files stored in DATA_DIR/backups/
- Settings: backup_enabled, backup_interval_hours, backup_retention_count
- API: POST/GET/DELETE /api/backups, download, restore endpoints
- Autobackup via cron scheduler with configurable interval
- Retention: prune on startup, after each backup (manual and auto)
- Orphan cleanup: removes backup files without metadata on startup
- Restore: replaces DB and triggers graceful server shutdown
- Settings UI: /settings/backup with toggle, interval, retention config
- Backup list with download, delete, restore actions
- i18n: English and Russian translations

web/src/lib/i18n/en.json

@@ -204,6 +204,7 @@
     "registries": "Registries",
     "credentials": "Credentials",
     "authentication": "Authentication",
+    "backup": "Backups",
     "appearance": "Appearance",
     "staleThreshold": "Stale threshold (days)",
     "staleThresholdHelp": "Containers inactive for longer than this will be flagged as stale."
@@ -325,6 +326,44 @@
     "registriesLink": "Registries",
     "registryTokensSuffix": "section. Each registry stores its token encrypted in the database."
   },
+  "settingsBackup": {
+    "title": "Backup Management",
+    "description": "Manage database backups and configure automatic backup schedules.",
+    "autoBackup": "Automatic Backups",
+    "autoBackupHelp": "Automatically create backups at the configured interval.",
+    "interval": "Backup Interval",
+    "intervalHelp": "How often to create automatic backups.",
+    "intervalHours": "{hours} hours",
+    "retention": "Retention Count",
+    "retentionHelp": "Maximum number of backups to keep. Oldest are deleted first.",
+    "backupNow": "Backup Now",
+    "creatingBackup": "Creating...",
+    "backupCreated": "Backup created successfully",
+    "backupFailed": "Failed to create backup",
+    "backupList": "Backups",
+    "noBackups": "No backups yet. Create one manually or enable automatic backups.",
+    "columnFilename": "Filename",
+    "columnSize": "Size",
+    "columnType": "Type",
+    "columnDate": "Created",
+    "columnActions": "Actions",
+    "download": "Download",
+    "delete": "Delete",
+    "restore": "Restore",
+    "deleteConfirm": "Are you sure you want to delete this backup?",
+    "deleted": "Backup deleted",
+    "deleteFailed": "Failed to delete backup",
+    "restoreConfirm": "Are you sure you want to restore from this backup? This will replace the current database and restart the server. All current data will be lost.",
+    "restoreWarning": "This action cannot be undone!",
+    "restored": "Database restored. The server is restarting...",
+    "restoreFailed": "Failed to restore backup",
+    "typeManual": "Manual",
+    "typeAuto": "Auto",
+    "save": "Save",
+    "saving": "Saving...",
+    "saved": "Backup settings saved",
+    "saveFailed": "Failed to save backup settings"
+  },
   "settingsAuth": {
     "title": "Authentication Settings",
     "description": "Configure authentication mode and manage users.",