fix(backup): add lastBackup alias and totalBackups for frontend compatibility

The frontend expected `status.lastBackup` but the backend was returning
`status.lastRun`. This caused the backup dashboard to show "No backup available"
even when backups existed in the history.

Added:
- `lastBackup` as alias for `lastRun`
- `totalBackups` count of completed backups

backend/src/services/backupService.js

@@ -993,12 +993,16 @@ async function getBackupStatus(limit = 10) {
       }
     }
 
+    const lastRunWithManifest = lastRun ? { ...lastRun, manifestValid } : null;
+
     return {
       isRunning,
       isHealthy: Boolean(lastRun && lastRun.status === 'completed'),
-      lastRun: lastRun ? { ...lastRun, manifestValid } : null,
+      lastRun: lastRunWithManifest,
+      lastBackup: lastRunWithManifest, // Alias for frontend compatibility
       recentRuns: runs,
       recentBackups: runs, // Alias for frontend compatibility
+      totalBackups: runs.filter(r => r.status === 'completed').length,
       nextScheduledRun: getNextScheduledRun()
     };
   } catch (error) {