perf: eliminate full rescans with local caches; add queue tracking, notifications, SyncView redesign

Cached indexes:
- NASManifestCache: actor-based disk cache for the NAS manifest (kisani_manifest_cache.json)
  Avoids NAS network round-trip when cache < 5 min old. Updated after every manifest download.
- LocalPhotoIndex: actor-based disk cache of phone asset metadata (kisani_local_index.json)
  Built once on first launch, then updated incrementally via PHPhotoLibraryChangeObserver.
  O(1) countSafe via in-memory dict (vs PHFetchResult batch enumeration + CoreData calls).

Fast path reconcile:
  When both caches are warm, reconcile() skips NAS connection + PHFetchResult enumeration
  entirely and returns in microseconds. Falls through to full NAS path only when stale.

AutoBackupCoordinator.onActive():
  Changed force: true → force: false so the 30-second debounce prevents expensive rescans
  on rapid app foreground/background cycles. Dashboard appears instantly from cached snapshot.

BackupQueueItem + queue tracking:
  BackupEngine publishes queueItems: [BackupQueueItem] with per-file status, progress,
  speed, error details. Queue is persisted to disk and reloaded on next launch so SyncView
  always has data to show even after restart.

NotificationService:
  Centralised local notification sender replacing the inline UNMutableNotificationContent
  blocks. Sends for: backup started, completed, failed, paused, NAS offline. Uses category
  identifiers so same-type notifications replace each other.

SyncView redesign:
  - Removed pill/chip around NAS IP — replaced with plain "Online/Offline/Checking" dot+text
  - No live NAS directory listing (was expensive NAS connection on every tab open)
  - Shows engine.queueItems grouped into Active / Failed / Completed sections
  - Per-file rows with inline progress bar + bytes/speed for uploading items, error text for failed
  - Idle state shows archive count from statusService snapshot

GalleryViewModel:
  NAS tab and All tab now use NASManifestCache as fallback when statusService.lastManifest
  is nil (offline launch). Gallery shows NAS items even when NAS is unreachable.

AppDelegate:
  Bootstraps LocalPhotoIndex.loadOrBuild() in background on launch (non-blocking).

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

App/AppDelegate.swift

@@ -11,6 +11,11 @@ final class AppDelegate: NSObject, UIApplicationDelegate {
         BackgroundTaskManager.registerTasks()
         requestNotificationPermission()
         setupLANMonitor()
+        // Bootstrap local indexes in the background — non-blocking.
+        // After first build they're loaded from disk in microseconds.
+        Task(priority: .utility) {
+            await LocalPhotoIndex.shared.loadOrBuild()
+        }
         return true
     }