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

iso/Dockerfile

@@ -10,7 +10,7 @@ ENV DEBIAN_FRONTEND=noninteractive
 RUN apt-get update && apt-get install -y --no-install-recommends \
         bash git curl ca-certificates xz-utils tar patch python3 \
         mtools xorriso squashfs-tools dosfstools e2fsprogs \
-        kmod \
+        kmod dconf-cli \
     && rm -rf /var/lib/apt/lists/*
 
 # xbps-static is downloaded into /cache by the host script and added to PATH