Expose the system-config backup on demand (not just within 'backup all'):
- `libreportal backup system` -> backupSystemConfig (snapshot the system
config — settings, WebUI creds, backup-location creds — to all enabled locations)
- `libreportal restore system [loc_idx]` -> backupRestoreSystemConfig (restore the
latest system snapshot into a staging dir; never overwrites live config)
Distinct from the existing 'restore migrate system' (which restores all *apps*
from another host). Help text updated for both. Routing verified with stubs.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>
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