Add live backup status reconciliation with NAS manifest

BackupStatusService (new singleton, ObservableObject, PHPhotoLibraryChangeObserver):
- Loads cached BackupStatusSnapshot instantly from UserDefaults on init
- Full reconcile: fetch phone assets → connect NAS → load/build manifest → compare
  → enforce invariant (alreadySafe ≤ phoneTotal), persist result
- Debounced (30s) for photo library changes; force=true bypasses debounce
- If NAS unreachable: keeps last cached numbers, marks connectionState = .offline
- PHPhotoLibraryChangeObserver triggers refresh on any library change

BackupManifest (new):
- Stored at {remotePath}/.kisani.json on NAS
- Indexed by localIdentifier (PHAsset stable ID); filename fallback for legacy entries
- Built from directory listing if manifest missing (bootstrap for existing backups)
- merged/updated after each backup run via NASTransferProtocol.writeData

BackupStatusSnapshot (new):
- Single source of truth: phoneTotal, alreadySafe, needBackup (derived), nasArchiveTotal,
  lastCheckedAt, connectionState
- Invariant enforced in service: alreadySafe = min(safe, phoneTotal)

Protocol / services:
- NASTransferProtocol: adds writeData(_ data: Data, to remotePath: String)
- SMBService: implements writeData via temp file + SMBClient.upload
- SFTPService: implements writeData via SFTP ByteBuffer write

BackupEngine:
- Tracks ManifestEntry per successful upload during backup loop
- After backup: calls BackupStatusService.refreshAfterBackup(entries:connection:)
  which applies optimistic UI update then writes manifest + triggers reconcile

BackupView:
- Reads all stats from BackupStatusService.snapshot (not vm/nasFileCount)
- Stats labels: "NAS Archive" / "On iPhone" / "Need Backup" / "Already Safe"
- Live refresh triggers: .task (force), scenePhase.active (force),
  nasReachable change (force), remotePath change (force), backup completed (+2s)
- Subtle status row below stats: "Checking…" spinner or "Updated X ago" with
  wifi-slash icon when NAS offline; tap refresh button for forced reconcile
- AppMenuView sheet now correctly passes engine EnvironmentObject

BackupViewModel: stripped to auth-only (photosAuthStatus + requestPhotosAccess)

Co-Authored-By: Kutesir <kutesir@provoc.ug>
Co-Authored-By: Sentry <sentry@provoc.ug>

Services/BackupEngine.swift

@@ -81,6 +81,7 @@ final class BackupEngine: ObservableObject {
         var failed = 0
         var totalBytes: Int64 = 0
         var speedTracker = SpeedTracker()
+        var manifestEntries: [ManifestEntry] = []
 
         // 4. Transfer loop
         for asset in assets {
@@ -119,6 +120,15 @@ final class BackupEngine: ObservableObject {
                 totalBytes += fileSize
                 job.fileCompleted(skipped: false)
                 uploaded += 1
+
+                manifestEntries.append(ManifestEntry(
+                    localIdentifier: asset.localIdentifier,
+                    filename: asset.filename,
+                    creationDate: asset.creationDate,
+                    fileSize: fileSize,
+                    remotePath: remotePath,
+                    uploadedAt: Date()
+                ))
             } catch {
                 logger.error("Upload failed for \(asset.filename, privacy: .public): \(error.localizedDescription, privacy: .public)")
                 job.fileFailed()
@@ -138,6 +148,9 @@ final class BackupEngine: ObservableObject {
 
         job.finish(result: result)
 
+        // Update manifest and dashboard status
+        BackupStatusService.shared.refreshAfterBackup(entries: manifestEntries, connection: connection)
+
         let entry = BackupHistoryEntry(result: result, nasHost: host, triggeredByLAN: triggeredByLAN)
         store.appendHistoryEntry(entry)