Fix audio/video continuing after window close and window close failures

[Copilot]

Audio and video continue playing after closing windows with multiple frames. Additionally, windows fail to close properly, appearing hidden but remaining in the Window menu. The existing stopMediaPlayback() only used asynchronous JavaScript, which doesn't execute before QWebEnginePages are destroyed.

Changes

SplitFrameWidget::stopMediaPlayback()

• Add synchronous setAudioMuted(true) to immediately stop audio output
• Retain async JavaScript cleanup for completeness
• Removed setLifecycleState(Frozen) - was preventing proper page cleanup and causing window close failures

void SplitFrameWidget::stopMediaPlayback() {
  if (!webview_ || !webview_->page()) return;
  
  QWebEnginePage *page = webview_->page();
  page->setAudioMuted(true);                                // Immediate
  page->runJavaScript("/* pause/clear media elements */");  // Async
}

The two-layer approach ensures audio stops immediately while avoiding lifecycle freezing that interferes with Qt's window destruction. Critical for live streams and incognito mode.

Issues Fixed

1. Media playback continues after window close - Synchronous audio muting stops playback immediately
2. Window close failures - Removing lifecycle freeze allows proper window destruction and cleanup

Documentation

• Updated AGENTS.md with implementation details and note about avoiding lifecycle freezing
• Updated method documentation in SplitFrameWidget.h

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Audio [and possibly "hidden" video?] keeps playing after closing window with multiple active frames</issue_title>
<issue_description>## Bug report
When audio/video is playing in multiple frames, closing the window does not stop playback. Audio continues (and likely the hidden video too) even though the window is closed.

Steps to reproduce

1. Open a window and create multiple frames (split panes).
2. Start audio/video playback in two or more frames.
3. Close the window.

Expected behavior

Closing the window stops all media playback for its frames.

Actual behavior

Audio continues playing after the window is closed (video likely still playing offscreen).

Notes

• Happens when multiple frames are playing media.
• May indicate the underlying QWebEngine profiles/pages are not being torn down on window close.</issue_description>

Comments on the Issue (you are @copilot in this section)

@paulpv This is still happening, especially if there is a video playing that is a live stream and in incognito mode.

• Fixes Audio [and possibly "hidden" video?] keeps playing after closing window with multiple active frames #58

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[paulpv]

@copilot The previous code also had the problem that if the window closing failed then the window would still stay open (but seemed hidden/minimized) and show in the Window menu and could be foregrounded again... at which point closing a 2nd time would also fail and still seem hidden/minimized and still show in the Window menu... and the process repeats.

That seems like a different problem than what this PR fixes.
Fix that problem in this PR too.

[Copilot]

@copilot The previous code also had the problem that if the window closing failed then the window would still stay open (but seemed hidden/minimized) and show in the Window menu and could be foregro...

Fixed in commit 8baab52. The issue was caused by setLifecycleState(Frozen) preventing proper page cleanup during window close. Removed that call - now using only synchronous audio muting + async JavaScript cleanup. Windows should now close properly without appearing hidden/minimized in the Window menu.

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