iOS local downloads fail for BBC episodes using signed CDN redirects #1035

Environment

• PinePods server: 0.9.0
• PinePods iOS app: 0.9.0
• Feed: BBC Composer of the Week
  https://podcasts.files.bbci.co.uk/p02nrvd3.rss

Problem

BBC episodes stream successfully in the iOS app when connected through a UK VPN, but “Download locally” consistently ends with “Local download failed.”

Tested with both an older Chopin episode and recent episodes. Other podcasts download normally.

Findings

BBC’s permanent media URL redirects to a temporary Akamai CDN URL. That URL appears network/geolocation-sensitive:

• A ranged request from the network that obtained the URL returned 206 audio/mpeg.
• The same signed URL requested from another network returned 403.
• The iOS app’s streaming works through the UK VPN, but its local downloader still fails.

In mobile_download_service.dart, resolveUrl() follows redirects first and then passes the final signed URL to flutter_downloader. On iOS, that hands the URL to a separate background URLSession, which may use a different network context from the one that obtained the signed URL.

Could the iOS downloader pass the permanent all-HTTPS BBC selector URL directly to URLSession and let that session follow the redirects itself, instead of pre-resolving the signed CDN URL?

The app currently records only FAILED, without exposing the native download error.

Related: #950