fix: TypeScript-Fehler im Frontend beheben

- AudioPlayer: findLast → reverse().find() (ES2022 Kompatibilität)
- ChapterList: findLastIndex → manuelles for-loop + implizit any behoben
- Library: searchDebounce Variable 't' undefined → korrekte Initialisierung

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

frontend/src/components/player/AudioPlayer.tsx

@@ -115,7 +115,7 @@ export default function AudioPlayer() {
       : `${m}:${sec.toString().padStart(2, '0')}`
   }
 
-  const currentChapter = chapters.findLast?.((c: any) => currentTime >= c.start) || chapters[0]
+  const currentChapter = [...chapters].reverse().find((c: any) => currentTime >= c.start) || chapters[0]
 
   const addBookmark = async () => {
     if (!item) return

frontend/src/components/player/ChapterList.tsx

@@ -17,7 +17,10 @@ export default function ChapterList({ chapters, currentTime, onSeek }: Props) {
       : `${m}:${sec.toString().padStart(2, '0')}`
   }
 
-  const active = chapters.findLastIndex?.((c) => currentTime >= c.start) ?? -1
+  let active = -1
+  for (let i = 0; i < chapters.length; i++) {
+    if (currentTime >= chapters[i].start) active = i
+  }
 
   return (
     <div className="mt-4 border-t border-white/10 pt-4 max-h-64 overflow-y-auto">

frontend/src/pages/Library.tsx

@@ -50,8 +50,8 @@ export default function Library() {
 
   const searchDebounce = useCallback(
     (() => {
-      let t: ReturnType<typeof setTimeout>
-      return (v: string) => { clearTimeout(t); setSearch(v); setPage(0) }
+      let t: ReturnType<typeof setTimeout> | undefined
+      return (v: string) => { clearTimeout(t); t = setTimeout(() => { setSearch(v); setPage(0) }, 300) }
     })(),
     []
   )