fix(dl): resolve download links in arr (#100)

Transmission has no route to Prowlarr, and Prowlarr redirects a
.torrent link to a magnet that a file fetch cannot follow. arr fetches
the link itself and sends Transmission a magnet or the torrent bytes.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

crates/arr-dl/src/lib.rs

@@ -16,12 +16,14 @@ const CONNECT_TIMEOUT: Duration = Duration::from_secs(5);
 const REQUEST_TIMEOUT: Duration = Duration::from_secs(30);
 
 /// Where Transmission is to get the torrent from.
+///
+/// Deliberately not an indexer URL: Transmission has no route to Prowlarr and
+/// cannot follow its redirect to a magnet, so arr resolves the link itself and
+/// hands over the result (issue #100).
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum TorrentSource {
     Magnet(String),
-    /// An HTTP link to a `.torrent`, fetched by Transmission itself. Indexer
-    /// download links arrive in this form.
-    Url(String),
+    /// The bytes of a `.torrent` file, sent inline.
     Metainfo(Vec<u8>),
 }
 
@@ -162,7 +164,7 @@ impl TransmissionClient {
         });
 
         match request.source {
-            TorrentSource::Magnet(uri) | TorrentSource::Url(uri) => {
+            TorrentSource::Magnet(uri) => {
                 arguments["filename"] = json!(uri);
             }
             TorrentSource::Metainfo(bytes) => {