feat: live ISO — nix daemon mode, autologin fix, GPU detection, app stack

- Switch nix from single-user to daemon mode (trusted-users = root live);
  Void socket at /var/nix/daemon-socket/socket confirmed
- Fix lightdm autologin: use session-wrapper=/etc/lightdm/Xsession (Void
  lightdm 1.32 has no lightdm-session binary)
- Fix session env: LIBGL_ALWAYS_SOFTWARE=1 via profile.d (session-env=
  is unsupported in this lightdm version)
- GPU auto-detection at boot: VIRT→software GL, NVIDIA PRIME offload,
  Intel/AMD/generic→modesetting
- Add nix-daemon to live runsvdir/default; remove unsupported -S mklive flag
- first-login.sh: install Claude Code + nix user packages (google-chrome,
  spotify, discord, localsend, mission-center) + NVM/node + VS Code exts
- build-live-iso.sh: write nix-packages.list from NIX_USER_PACKAGES
- postinstall.sh: fix nix-daemon socket path to /var/nix/daemon-socket/socket
- Dockerfile: add dconf-cli for build-time dconf compile
- _inner-build-live.sh: use correct 'dconf compile' API (not 'dconf update')
- .gitignore: add build/live-includes/ (generated staging tree)
- docs/LIVE_ISO.md: document all findings, gotchas and architecture

config/profiles/stable-cinnamon/packages.live-desktop.list

@@ -8,7 +8,6 @@ base-system
 linux
 linux-firmware
 linux-firmware-network
-intel-ucode
 dracut
 
 # --- core userspace ---
@@ -61,15 +60,20 @@ xorg-fonts
 xorg-input-drivers
 xf86-input-libinput
 xf86-video-intel
+xf86-video-fbdev
+xf86-video-vesa
 mesa-dri
 mesa-vulkan-intel
 intel-video-accel
 vulkan-loader
+pciutils
 
-# --- nvidia (PRIME offload) ---
+# --- nvidia (PRIME offload, from nonfree repo) ---
+# Installed so live-setup.sh can detect and configure PRIME at boot.
 nvidia
-nvidia-libs-32bit
+nvidia-libs
 nvidia-vaapi-driver
+# nvidia-vaapi-driver
 
 # --- desktop ---
 cinnamon