fix: Linux Electron UX improvements

[Flo0806]

Problems

1. Auto-update download works but install doesn't - "Restart Now" button does nothing on Linux. AppImage can't self-replace. Should show "Open Downloads" or link to release page instead.

2. Taskbar icon shows generic settings icon on Wayland - Electron 39 + NVIDIA crashes on Wayland, forcing X11 fallback via --ozone-platform=x11. XWayland windows don't get proper WM_CLASS matching, so the desktop can't show the app icon.

3. Must start with CLI flags - Users need --ozone-platform=x11 --no-sandbox on Wayland+NVIDIA systems. Should detect and apply automatically, or document clearly.

4. Electron 39 SIGSEGV on Wayland+NVIDIA - Known upstream issue ([Bug]: node_modules/electron/dist/electron exited with signal SIGSEGV electron/electron#41980, closed as "Not planned"). Affects NVIDIA driver 590+ with Wayland. Works fine on X11 and on Electron 38.

Potential Solutions

• Detect Wayland+NVIDIA and auto-apply X11 fallback in AppImage wrapper script
• Replace "Restart Now" with "Open Release Page" on Linux
• Consider Electron 38 for Linux builds (Wayland works natively)
• Create .desktop file installer for proper system integration
• Monitor upstream Chromium/NVIDIA fixes