Fix HLS playback auth + add DNB matching source

Player: hls.js did not send Authorization header for segment requests,
causing 401 errors on all HLS fetches. Fixed via xhrSetup callback.

DNB: Added Deutsche Nationalbibliothek SRU search (mat=ton filter for
audiobooks, MARC21-XML parsing). Extracts title, author, narrator,
publisher, year, series, genres, ISBN-based cover URL.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/player/AudioPlayer.tsx

@@ -38,7 +38,13 @@ export default function AudioPlayer() {
 
     const audio = audioRef.current
     if (Hls.isSupported()) {
-      const hls = new Hls({ startPosition: session.currentTime || 0 })
+      const token = localStorage.getItem('token')
+      const hls = new Hls({
+        startPosition: session.currentTime || 0,
+        xhrSetup: (xhr: XMLHttpRequest) => {
+          if (token) xhr.setRequestHeader('Authorization', `Bearer ${token}`)
+        },
+      })
       hls.loadSource(hlsUrl)
       hls.attachMedia(audio)
       hlsRef.current = hls