feat: blur, transparency, focus mode & performance optimizations

[postadelmaga]

Summary

• Browser spoofing: Chrome 130 UA + navigator properties for auth page compatibility (Google, Claude, etc.)
• CSS transparency/blur: heuristic DOM analysis applies layered rgba + backdrop-filter to background elements
• Focus mode: per-site CSS rules + heuristic fallback hiding nav/aside/sidebar for clean chat view
• Visual options: accent glow border, header gradient, animation controls, overlay opacity
• WebEngine lifecycle: keep-alive option for instant reopen, or 5-min idle unload for memory saving
• Keyboard shortcuts: Enter-to-send for DuckDuckGo, ChatGPT, Gemini, Claude, You
• Session restore: last visited URL persists across WebView unload/reload
• Fix: remove ContextMenu.qml — uses PlasmaExtras.Menu/MenuItem which don't exist in Plasma 6; PlasmaComponents3.Menu can't be a root type in a separate file. Context menu is now inline in WebView.qml.

Performance optimizations

Fix	Impact
Pre-built JS injection strings (readonly property)	Zero string rebuild per page load
Batch DOM reads before writes in blur injection	Eliminates layout thrashing (N-1 forced reflows)
MutationObserver replaces setInterval(100ms) for textarea focus	From ~50 timer fires/5s to 0
Narrowed focus mode selectors (body > div vs div, section)	~95% fewer elements scanned
Debounced renderChatModel + single-pass customSites parsing	Coalesces N config toggles into 1 render
Accent glow wrapped in Loader	Zero QML objects when disabled
Header animations gated on enableAnimations && autoHideHeader	Zero animation overhead when not needed
Download signal cleanup on Component.onDestruction	Prevents connection leaks

Test plan

• Toggle blur on/off — transparency applies/removes correctly
• Enable focus mode on ChatGPT, Claude, DuckDuckGo, Gemini — sidebars hidden
• Focus mode on unknown site — heuristic fallback hides nav/aside elements
• Auto-hide header — shows on hover, hides on mouse leave, stays during ComboBox interaction
• Enter key sends message on compatible sites (DuckDuckGo, ChatGPT, Gemini, Claude)
• Accent glow border toggle on/off
• Keep WebEngine alive: close widget, reopen — page still loaded
• Download a file — progress bar works, no console errors on widget close during download
• Browser spoof: login to Google-auth sites works
• Right-click context menu works (back, forward, reload, save, open link)

[DenysMb]

Hey! Thank you for the contribution.

I didn't like the idea of this blur feature making changes in the DOM, it can significantly affect the issue of accessibility.
Even if we made it optional by default, it would be very laborious to maintain, as we would have to ensure proper functioning across various services.
In my tests with some services, the result was not good in many of them, with only part of the sites having blur.

Furthermore, the changes to browser spoofing not only failed to resolve the authentication problem with Claude, but also caused several other services to stop working, making it no longer possible to authenticate with Google.

I like the idea of ​​making changes to improve performance and address minor issues we might have, but I didn't like the two I mentioned above.

If you still decide to contribute, I recommend a PR focused solely on performance issues.