refactor: Use chroot instead of systemd-nspawn for workspace entry

- Replace systemd-nspawn with chroot to avoid nested container audit errors
- Add manual bind mount setup for /home/ai:/root sharing
- Add mount and chroot to sudoers permissions
- chroot avoids kernel audit subsystem conflicts in nested containers

cfg/setup-user.sh

@@ -75,7 +75,11 @@ if [[ -o login ]] && [[ -o interactive ]]; then
     if [[ -z "$INSIDE_WORKSPACE" ]]; then
         # Running as ai user on aios OS - enter workspace container
         export INSIDE_WORKSPACE=1
-        exec sudo systemd-nspawn -q -D /var/lib/machines/workspace /bin/zsh
+        # Setup bind mount for shared user directory
+        sudo mkdir -p /var/lib/machines/workspace/root 2>/dev/null || true
+        sudo mount --bind /home/ai /var/lib/machines/workspace/root 2>/dev/null || true
+        # Enter workspace via chroot (avoiding nested systemd-nspawn audit issues)
+        exec sudo chroot /var/lib/machines/workspace /bin/zsh
     else
         # Running as root inside workspace container - start claude
         if command -v claude &>/dev/null; then