Enable restoring PVs

[YektaY]

Currently squirrel frontend only has a placeholder for restoring PVs.

The backend does have an API Endpoint: POST /v1/snapshots/{snapshot_id}/restore
This is untested.
the restore logic in the backend can be seen at app/services/epics_service.py

placeholder in src/routes/snapshot-details.tsx:

  const handleRestore = useCallback((pvs: PV[]) => {
    console.log('Restoring PVs:', pvs);
    alert(`Restoring ${pvs.length} PV(s) - This feature is not yet implemented`);
  }, []);

[tiffany-slac]

• Give users feedback that they can safely navigate away from the screen while the restore is in progress
• Keep the interaction consistent with the save snapshot flow by reusing similar notification component
• Move the restore notification above the line (instead of below the line by the “Save Snapshot” button) to keep things consistent in this context
• Since restore is a more critical action, give it more prominent feedback by adding a bottom status panel to show more detailed restore progress
• Let users expand/collapse/close the status panel so they have control over how much detail they see
• Design leaves room for a potential “cancel restore” action