KDE Plasma 6.6 Beta: New Login Manager, USB Portal and Wayland improvements

Key points:

• Introduce plasma-login-manager as a modern replacement for SDDM.
• New virtual plasma-keyboard and OEM plasma-setup wizard.
• Critical improvements in Wayland: XRandr emulation and reliable screen mirroring.
• USB portal for security in isolated apps and OCR support in Spectacle.
• Accessibility controls for edge contrast and Wi-Fi connection via QR code.