Add Backup Management GUI (Phase 3-4)

Web GUI Implementation:
- Backup.vue: Storage dashboard + Snapshot management + Scheduler config
- Router: Add /backup route
- Home.vue: Add Backup management card
- Tauri commands: 10 backup API endpoints

Features:
- Storage stats (total/used/free, dedup/compression ratios)
- Snapshot list with create/delete/restore actions
- Backup scheduler configuration (enabled, interval, max_snapshots)
- Run backup now button
- Send/Receive placeholders

Tauri Commands:
- get_storage_stats, list_snapshots
- create_snapshot, delete_snapshot, restore_snapshot
- get_backup_stats, get_backup_config, set_backup_config
- run_backup

Build: cargo build (Tauri) ✅ 5 warnings
Tests: 495 markbase-core + 201 smb-server = 696 total

markbase-tauri/src-tauri/src/main.rs

@@ -33,6 +33,15 @@ fn main() {
             list_users,
             run_health_check,
             get_monitor_data,
+            get_storage_stats,
+            list_snapshots,
+            create_snapshot,
+            delete_snapshot,
+            restore_snapshot,
+            get_backup_stats,
+            get_backup_config,
+            set_backup_config,
+            run_backup,
         ])
         .run(tauri::generate_context!())
         .expect("error while running tauri application");