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

installer/lib/postinstall.sh

@@ -206,14 +206,13 @@ mark=/var/lib/first-boot-nix.done
 [[ -f "\$mark" ]] && exit 0
 
 # Wait for nix-daemon to be available.
-# The Void package puts the socket at /var/nix/daemon-socket/nix-daemon.sock
-# (NOT /nix/var/nix/...).
-for _ in \$(seq 1 30); do
-    [[ -S /var/nix/daemon-socket/nix-daemon.sock ]] && break
-    sleep 1
+# The Void xbps nix package puts the socket at /var/nix/daemon-socket/socket.
+for _ in \$(seq 1 60); do
+    [[ -S /var/nix/daemon-socket/socket ]] && break
+    sleep 2
 done
 
-if [[ ! -S /var/nix/daemon-socket/nix-daemon.sock ]]; then
+if [[ ! -S /var/nix/daemon-socket/socket ]]; then
     echo "nix-daemon not available; aborting first-boot nix install" >&2
     exit 0
 fi