Add cellular data toggle, Tailscale remote access, fix ToggleRow padding

- ToggleRow: fix cramped layout — proper horizontal + vertical card padding
- ConnectionStore: add allowCellularBackup, useTailscaleWhenRemote, tailscaleHost
- LANMonitor: add isOnCellular (NWPath cellular interface), isTailscaleActive
  (detects utun interface with 100.x.x.x CGNAT address), openTailscaleApp()
- BackupEngine: gate backup on cellular setting; resolveHost() switches to
  tailscaleHost when not on trusted LAN and Tailscale tunnel is active
- SettingsView: CONNECTIVITY section (cellular toggle + live status),
  REMOTE ACCESS section (Tailscale toggle, host field, status dot, Open button)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Shared/Components/ToggleRow.swift

@@ -30,6 +30,7 @@ struct ToggleRow: View {
                 .labelsHidden()
                 .tint(AppTheme.ink)
         }
-        .padding(.vertical, 2)
+        .padding(.horizontal, AppTheme.cardPad)
+        .padding(.vertical, 12)
     }
 }