Fix backup loop, phone count invariant, and auto-start behaviour

- LocalPhotoIndex: add count(filter:) so fast-path reconcile uses the
  filtered asset count as phoneTotal instead of the unfiltered totalCount;
  fixes the broken alreadySafe + needBackup == phoneTotal invariant

- BackupStatusService: fast-path uses count(filter:) instead of totalCount;
  writeManifest falls back to NASManifestCache when NAS download fails so
  accumulated history is never silently discarded on a flaky connection

- ConnectionStore: autoBackupEnabled defaults false; new autoBackupOnOpen
  (default false) separates LAN-join auto-backup from app-open auto-backup

- AutoBackupCoordinator: onActive(lanTriggered:) tracks trigger source;
  handleReconciliationComplete gates on autoBackupEnabled for LAN joins and
  autoBackupOnOpen for app-open — prevents backup starting on every launch

- SettingsView: split auto-backup into two toggles with accurate descriptions

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

Shared/Persistence/ConnectionStore.swift

@@ -63,11 +63,16 @@ final class ConnectionStore: ObservableObject {
         didSet { UserDefaults.standard.set(localRetentionDays, forKey: "localRetentionDays") }
     }
 
-    // Auto-backup: default on after first destination is configured
+    // Auto-backup via LAN trigger (trusted Wi-Fi join)
     @Published var autoBackupEnabled: Bool {
         didSet { UserDefaults.standard.set(autoBackupEnabled, forKey: "autoBackupEnabled") }
     }
 
+    // Auto-backup on every app open — off by default; requires explicit opt-in
+    @Published var autoBackupOnOpen: Bool {
+        didSet { UserDefaults.standard.set(autoBackupOnOpen, forKey: "autoBackupOnOpen") }
+    }
+
     // Cellular & remote access
     @Published var allowCellularBackup: Bool {
         didSet { UserDefaults.standard.set(allowCellularBackup, forKey: "allowCellularBackup") }
@@ -94,7 +99,8 @@ final class ConnectionStore: ObservableObject {
         onboardingPhotoShown   = UserDefaults.standard.bool(forKey: "onboardingPhotoShown")
         appearanceMode         = AppearanceMode(rawValue: UserDefaults.standard.string(forKey: "appearanceMode") ?? "") ?? .system
         localRetentionDays     = UserDefaults.standard.object(forKey: "localRetentionDays") as? Int ?? 0
-        autoBackupEnabled      = UserDefaults.standard.object(forKey: "autoBackupEnabled") as? Bool ?? true
+        autoBackupEnabled      = UserDefaults.standard.object(forKey: "autoBackupEnabled") as? Bool ?? false
+        autoBackupOnOpen       = UserDefaults.standard.object(forKey: "autoBackupOnOpen") as? Bool ?? false
         allowCellularBackup    = UserDefaults.standard.object(forKey: "allowCellularBackup") as? Bool ?? false
         useTailscaleWhenRemote = UserDefaults.standard.object(forKey: "useTailscaleWhenRemote") as? Bool ?? false
         tailscaleHost          = UserDefaults.standard.string(forKey: "tailscaleHost") ?? ""