feat: Big Picture on NVIDIA starts on an empty Plasma session, so restored windows don't cover it

CHANGELOG.md

@@ -7,7 +7,7 @@ one per merged pull request.
 
 ## 2.9.7 - 2026-10-01
 
-- **feat: "Gaming on NVIDIA" (nvidia) replaces the SteamOS conversion on PCs with an NVIDIA GPU, where gamescope's gaming mode shows a corrupted picture (NVIDIA bug 5240452): Steam is installed when missing and starts at login on the Plasma desktop; the sub-option "Steam starts in Big Picture" (bigpicture, ticked along with it) starts it in Big Picture, unticked in its normal window (lib/nvidia.sh, services/steamify-steam-autostart.service). On a supported card (RTX 20 series or newer, chwd's legacy lists like the VRAM booster) it also puts nvidia-drm.modeset=1 and fbdev=1 on the kernel command line (Limine incl. its `+=` line, systemd-boot, GRUB) and the NVIDIA modules in the initramfs while every installed kernel has them (a pacman hook decides at every kernel change). The conversion and its options are hidden there unless already on**
+- **feat: "Gaming on NVIDIA" (nvidia) replaces the SteamOS conversion on PCs with an NVIDIA GPU, where gamescope's gaming mode shows a corrupted picture (NVIDIA bug 5240452): Steam is installed when missing and starts at login on the Plasma desktop; the sub-option "Steam starts in Big Picture" (bigpicture, ticked along with it) starts it in Big Picture, unticked in its normal window, and Big Picture starts on an empty Plasma session (no windows of the last session on top of it) (lib/nvidia.sh, services/steamify-steam-autostart.service). On a supported card (RTX 20 series or newer, chwd's legacy lists like the VRAM booster) it also puts nvidia-drm.modeset=1 and fbdev=1 on the kernel command line (Limine incl. its `+=` line, systemd-boot, GRUB) and the NVIDIA modules in the initramfs while every installed kernel has them (a pacman hook decides at every kernel change). The conversion and its options are hidden there unless already on**
 - **feat: single user mode also works on NVIDIA PCs, without the SteamOS conversion: it switches to SDDM and logs in to the Plasma session by itself (/etc/sddm.conf.d/zzz-steamify-autologin.conf), and no longer ticks the conversion where that isn't offered (lib/single-user.sh)**
 - **test: tests/nvidia-test.sh runs it against a fake RTX 5080 beside an iGPU, a stub pacman and systemctl, and a temp home (no root, VM or hardware); verified on a real RTX 5080: gamescope's session, a nested gamescope and a KWin-only session all showed artifacts or stutter, Big Picture on the Plasma desktop did not**