fix(web player + stats modal): no auto-resume after user pause; stable stats modal

Player: opening the PWA no longer auto-plays when the user had paused. Pausing via
the media notification while backgrounded routes through togglePlay, which now sets
S._userPaused; _onForeground only auto-resumes an INVOLUNTARY background stop
(_wasPlayingBeforeHide && !_userPaused). playCurrent clears the flag on a new track.
Involuntary-stop/freeze recovery on foreground is preserved.

Stats modal: no more small→big flash when switching period/tab — the body keeps a
stable min-height and retains its current content until the new data arrives (only
the first open shows 'Lade…'); a per-request token drops out-of-order responses.
SW cache -> ns-v71.

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

src/main.js

@@ -202,10 +202,12 @@ window.addEventListener('load', () => {
     // Skip when native is active: Media3 owns the system media session.
     if(navigator.mediaSession && !S._trackChanging && !window.NSBridge)
       navigator.mediaSession.playbackState = S.audio.paused ? 'paused' : 'playing';
-    // Only auto-resume if audio was actually playing when the page hid (OS-killed buffer).
-    // If the user explicitly paused, _wasPlayingBeforeHide is false — don't restart.
+    // Only auto-resume after an INVOLUNTARY background stop (OS-killed buffer / frozen tab).
+    // Never restart if the user deliberately paused — including via the media notification while
+    // backgrounded (that routes through togglePlay → S._userPaused=true), which used to wrongly
+    // auto-resume on foreground because _wasPlayingBeforeHide was still true from hide-time.
     if(!S.audio.paused) return;
-    if(s && S.audio.src && _wasPlayingBeforeHide) S.audio.play().catch(() => { S._trackChanging = false; });
+    if(s && S.audio.src && _wasPlayingBeforeHide && !S._userPaused) S.audio.play().catch(() => { S._trackChanging = false; });
   }
 
   document.addEventListener('visibilitychange', () => {