feat(app,android,ios): ask before forgetting matches or downloading a whole show

- Turning metadata off or switching provider forgets every stored answer,
  including matches chosen by hand. The desktop now asks first and says
  how many hand-picked matches go. The phones' settings dialog says so
  above Save.
- Forgetting a hand-picked match on the desktop, and any match on the
  phones, is asked about first.
- Downloading a season, a show, or everything from a library tile asks
  first, with the episode count and their size.
- Android confirmations that delete something use an error-toned text
  button rather than the filled accent, which read as the safe choice.

ios/ProtonStream/UI/SettingsView.swift

@@ -329,6 +329,13 @@ private struct MetadataSettingsSheet: View {
             if enabled, provider == .tmdb, !current.ready, apiKey.trimmingCharacters(in: .whitespaces).isEmpty {
                 Text("Enter a TMDB API key to save.").foregroundStyle(scheme.error)
             }
+            // Said before Save rather than after: what is forgotten includes
+            // matches chosen by hand, which no look-up redoes.
+            if current.enabled, !enabled || provider != current.provider {
+                Text("Saving forgets every poster, description and match stored now, including ones you chose by hand.")
+                    .textStyle(.bodySmall)
+                    .foregroundStyle(scheme.error)
+            }
             if let refusal {
                 Text(refusal).foregroundStyle(scheme.error)
             }