backup/ held 15 loose .js plus css/html at the component root. Split into
per-tab sub-systems mirroring the admin/apps layout:
backup/core/{js,css,html}/ schema, base BackupPage, fetch-client,
cron-schedule, backup.css, backup-content.html
backup/dashboard/js/ backup-dashboard
backup/snapshots/js/ backup-snapshots, backup-snapshot-actions
backup/locations/js/ backup-locations, backup-location-fields,
backup-location-modal, backup-ssh-key
backup/migrate/js/ backup-migrate
backup/configuration/js/ backup-configuration, backup-retention-presets,
backup-engine-details
Updated the scripts[] array + loadFragment in index.js, the backup.css href in
index.html, and the handleBackup() fallback paths in spa.js. No behaviour
change — files moved verbatim (prototype-augment clusters), all 17 referenced
paths verified to resolve, node --check clean.
Signed-off-by: librelad <librelad@digitalangels.vip>