v0.8.1 — fix plasmalogin / display-manager detection

Bug fix.

--caelestia mode detection now also checks display-manager.service (the canonical alias every DM symlinks to) and plasmalogin explicitly. CachyOS-Plasma uses KDE's rebranded plasmalogin.service instead of stock sddm.service; previous check missed it and only the wayland-sessions fallback (plasma.desktop) saved us from misclassifying as fresh mode.