Do not auto-download enclosures that are not audio or video

Blog feeds put each article's header image in an <enclosure>, so a text
feed read as a podcast full of episodes: 149 images, 74 MB across 11
feeds. media_types defaults to audio and video, with a per-feed override.

Such enclosures stay listed and stay downloadable by hand; the row names
what it is rather than saying "skipped". An unknown type is allowed, since
the real type is only known after downloading, and a torrent is allowed as
a container judged once unpacked.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AdXho5tTkjFLeUXKbEjKBh

src/download.rs

@@ -385,7 +385,7 @@ mod tests {
         let mut cfg = Config::default();
         cfg.general.download_dir = "/tmp".into();
         let mut f = crate::config::Feed {
-            url: "u".into(), folder: Some("Subscriptions/Some | Show".into()), group: None,
+            url: "u".into(), folder: Some("Subscriptions/Some | Show".into()), group: None, media_types: None,
             schedule: None, keywords: vec![], allow_explicit: false, auto_download: true,
             max_new_per_check: None, username: None, password: None, password_env: None,
         };