refactor: replace playback-initiated ref with conditional IPC subscription

A mutable ref guarded AppShell's IPC listeners against events fired by
ChannelScreen's playback session. The ref had to be set and cleared in
five separate places, making the control flow hard to follow.

The two contexts are already mutually exclusive at the UI level, so the
guard is unnecessary. Subscribing only when no ChannelScreen is open
expresses the same invariant through React's effect lifecycle instead.

src/renderer/src/screens/AppShell.tsx

@@ -35,8 +35,6 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
   const [livePlayState, setLivePlayState] = useState<GlobalPlayState>('idle')
   const [livePosition, setLivePosition] = useState(0)
   const liveVideoRef = useRef<VideoPlayerHandle>(null)
-  // Verhindert dass ChannelScreen-Events den globalen Overlay aktivieren
-  const isGlobalPlaybackInitiated = useRef(false)
   // Quality state für globalen Overlay
   const [liveAvailableQualities, setLiveAvailableQualities] = useState<string[] | undefined>(undefined)
   const [liveCurrentQuality, setLiveCurrentQuality] = useState('best')
@@ -46,19 +44,14 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
 
   const isGlobalPlaying = livePlayState !== 'idle'
 
-  // IPC-Listener für globalen Playback (nur wenn kein ChannelScreen aktiv)
+  // IPC-Listener für globalen Playback — nur aktiv wenn kein ChannelScreen offen ist
   useEffect(() => {
-    const unsubHls = window.t4sd.playback.onHlsUrl((payload: HlsUrlPayload) => {
-      if (isGlobalPlaybackInitiated.current) {
-        setLiveHlsPayload(payload)
-      }
-    })
+    if (selectedChannel) return
+    const unsubHls = window.t4sd.playback.onHlsUrl(setLiveHlsPayload)
     const unsubEvent = window.t4sd.playback.onEvent((ev) => {
-      if (!isGlobalPlaybackInitiated.current) return
       if (ev.kind === 'started') {
         setLivePlayState('playing')
       } else if (ev.kind === 'stopped') {
-        isGlobalPlaybackInitiated.current = false
         setLiveHlsPayload(null)
         setLivePlayState('idle')
         setLiveChannel(null)
@@ -68,7 +61,6 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
         setLiveQualityPanelOpen(false)
         setLiveErrorMsg('')
       } else if (ev.kind === 'error') {
-        isGlobalPlaybackInitiated.current = false
         setLiveHlsPayload(null)
         setLivePlayState('error')
         setLiveErrorMsg(ev.message ?? 'Stream konnte nicht gestartet werden.')
@@ -77,7 +69,7 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
       }
     })
     return () => { unsubHls(); unsubEvent() }
-  }, [])
+  }, [!!selectedChannel])
 
   const requestSidebar = useCallback(() => {
     const idx = SIDEBAR_ITEMS.findIndex((t) => t.key === tab)
@@ -109,7 +101,6 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
 
   // Direkt-Start: kein ChannelScreen — globaler Overlay startet sofort
   const handleStartLive = useCallback((ch: FollowedChannelInfo) => {
-    isGlobalPlaybackInitiated.current = true
     setLiveChannel(ch)
     setLivePlayState('starting')
     setLiveAvailableQualities(undefined)
@@ -124,7 +115,6 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
   }, [])
 
   const handleStopLive = useCallback(() => {
-    isGlobalPlaybackInitiated.current = false
     liveVideoRef.current?.stop()
     setLiveHlsPayload(null)
     setLivePlayState('idle')
@@ -394,7 +384,6 @@ export default function AppShell({ onLogout }: Props): JSX.Element {
                 onPaused={() => setLivePlayState('paused')}
                 onEnded={handleStopLive}
                 onError={() => {
-                  isGlobalPlaybackInitiated.current = false
                   setLiveHlsPayload(null)
                   setLivePlayState('error')
                   setLiveErrorMsg('Wiedergabefehler — Stream konnte nicht geladen werden.')