Swap shows only the new media, no guessed endings, quieter screen

- A swap stops the previous media at once; buffer counts only for the
  media the player holds (client) and the current mediaId (server), so
  the old video can no longer start the new one.
- The automatic frozen-picture reload is gone (false alarms on still
  scenes); Reload video stays.
- The "Next episode" pill shows only from a known ending.
- A web link's thumbnail is its cover, under the video's own name.
- While playing, the unread chip stays off the picture; chat pop-ups
  can be All / Only when paused / Off.
- Server fetch failures say when the server has no cookies.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/test/jellyfin_e2e_test.dart

@@ -301,9 +301,9 @@ void main() {
         a.toggleReady();
         await _poll(() => all.every((x) => x.playback.player.state.playing), 'playing again');
 
-        // Account holders see the "Next episode" prompt (this item is
-        // shorter than its 2 min lead); the guest cannot put it up.
-        await _poll(() => a.nextPromptVisible.peek(), 'next prompt');
+        // No known ending (no Outro segment, no ED chapter): no floating
+        // "Next episode" prompt mid-episode, only the card at the end.
+        expect(a.nextPromptVisible.peek(), isFalse);
         expect(b.nextPromptVisible.peek(), isFalse);
 
         // Alice and the guest pick English; it carries to the next episode.