Podcast / RSS feeds for the library (web, part 1)

Subscribe to the whole library or a single channel in any podcast/media
app.

- src/feed.rs: pure RSS 2.0 + iTunes-namespace renderer with absolute
  enclosure URLs, MIME-by-extension, HH:MM:SS durations, and a
  chrono-free RFC-2822 date (civil-date algorithm). Unit-tested
  (mime / escape / duration / date / render).
- web.rs: GET /feed.xml (whole library, newest first, capped at 300) and
  GET /feed/:platform/:handle (one channel); /api/feed-info returns the
  token for the UI. Enclosure + thumbnail URLs are absolute (derived from
  Host + X-Forwarded-Proto) and carry the feed token.
- Auth: a stable read-only `feed_token` (persisted setting) lets a
  tokenized `?token=` GET reach /feed*, /files, and /music-files even when
  a password is set — podcast clients can't do the cookie login. Scoped to
  reads of feeds + media; never /api mutations.
- Web UI: a "📡 Podcast feed" section in Settings (library URL + Copy) and
  a "📡 Feed URL" button in each channel's options dialog.

Integration tests cover the served RSS (enclosure path, MIME, pubDate),
the channel feed + 404, and the full token gate (401 without token once a
password is set, 200 with it, /files reachable with it). 127 tests pass.

Desktop URL display follows.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/api.rs

@@ -367,6 +367,67 @@ fn full_text_search_indexes_titles_and_descriptions() {
             "unrelated query must not hit");
 }
 
+#[test]
+fn podcast_feed_serves_rss_with_enclosures() {
+    if !have_curl() { eprintln!("skip: no curl"); return; }
+    let s = Server::start();
+    let chan = s.dir.join("ch/channels/Demo");
+    std::fs::create_dir_all(&chan).unwrap();
+    std::fs::write(chan.join("Cool Talk [vidXYZ].mp4"), b"fakevideo").unwrap();
+    std::fs::write(chan.join("Cool Talk [vidXYZ].info.json"),
+                   br#"{"duration":125.0,"upload_date":"20240102"}"#).unwrap();
+    assert_eq!(s.post("/api/rescan", "").0, 200);
+
+    let (code, body) = s.get("/feed.xml");
+    assert_eq!(code, 200, "{body}");
+    assert!(body.contains("<rss"), "is RSS: {body}");
+    assert!(body.contains("<title>Cool Talk</title>"), "item title present: {body}");
+    assert!(body.contains("<enclosure"), "has an enclosure: {body}");
+    assert!(body.contains("/files/channels/Demo/Cool%20Talk%20%5BvidXYZ%5D.mp4"),
+            "enclosure points at the media file: {body}");
+    assert!(body.contains(r#"type="video/mp4""#), "correct MIME: {body}");
+    assert!(body.contains("Tue, 02 Jan 2024"), "pubDate from upload_date: {body}");
+    // The channel feed works too.
+    assert_eq!(s.get("/feed/channels/Demo").0, 200);
+    // Unknown channel → 404.
+    assert_eq!(s.get("/feed/channels/Nope").0, 404);
+}
+
+#[test]
+fn podcast_feed_token_gates_access_when_password_set() {
+    if !have_curl() { eprintln!("skip: no curl"); return; }
+    let s = Server::start();
+    let chan = s.dir.join("ch/channels/Demo");
+    std::fs::create_dir_all(&chan).unwrap();
+    std::fs::write(chan.join("Talk [vidT].mp4"), b"x").unwrap();
+    assert_eq!(s.post("/api/rescan", "").0, 200);
+
+    // Grab the feed token (UI is unauthenticated until a password is set).
+    let (_, info) = s.get("/api/feed-info");
+    let token = field(&info, "token").expect("feed token").to_string();
+    assert!(!token.is_empty());
+
+    // Set a password — now the UI + API require auth.
+    let (code, _) = s.post("/api/settings", &format!(
+        r#"{{"transcode":false,"scheduler_enabled":false,"scheduler_interval_hours":24,
+            "max_concurrent":3,"use_bundled_ytdlp":false,"use_pot_provider":false,
+            "subtitles_enabled":false,"subtitles_auto":false,"subtitles_embed":false,
+            "subtitle_langs":"","subtitle_format":"","youtube_player_clients":"",
+            "sponsorblock_mode":"mark","convert_mode":"","convert_crf":23,"convert_preset":"",
+            "convert_audio_format":"","convert_keep_original":false,
+            "new_download_password":"hunter2"}}"#));
+    assert_eq!(code, 200);
+
+    // Feed without the token is now rejected…
+    assert_eq!(s.get("/feed.xml").0, 401, "feed must be gated once a password is set");
+    // …but the tokenized URL still works (a podcast client can't log in).
+    assert_eq!(s.get(&format!("/feed.xml?token={token}")).0, 200);
+    // A wrong token is rejected.
+    assert_eq!(s.get("/feed.xml?token=bogus").0, 401);
+    // The media mount is reachable with the token too (so enclosures load).
+    assert_eq!(s.get(&format!("/files/channels/Demo/Talk%20%5BvidT%5D.mp4?token={token}")).0, 200);
+}
+
 #[test]
 fn perceptual_dedup_groups_reencodes() {
     if !have_curl() { eprintln!("skip: no curl"); return; }