Fix learner-add.sh for NixOS compatibility

- Use 'users' group instead of per-user groups
- Remove shell specification (NixOS has different paths)
- Use 'ip' command instead of 'hostname -I' for IP detection

scripts/learner-add.sh

@@ -65,7 +65,8 @@ create_user() {
     log_info "Creating user '$username'..."
 
     # Create user with home directory
-    useradd -m -s /bin/bash "$username"
+    # NixOS: don't specify shell (uses default), group is 'users'
+    useradd -m -g users "$username"
 
     # Set up SSH key
     local ssh_dir="/home/$username/.ssh"
@@ -73,7 +74,7 @@ create_user() {
     echo "$ssh_key" > "$ssh_dir/authorized_keys"
     chmod 700 "$ssh_dir"
     chmod 600 "$ssh_dir/authorized_keys"
-    chown -R "$username:$username" "$ssh_dir"
+    chown -R "$username:users" "$ssh_dir"
 
     log_info "User created with SSH access"
 }
@@ -109,7 +110,7 @@ setup_plugin_directory() {
     fi
 
     # Set ownership
-    chown -R "$username:$username" "$user_plugins_dir"
+    chown -R "$username:users" "$user_plugins_dir"
 
     # Make plugin dir readable by maubot group
     chmod 755 "/home/$username"
@@ -243,7 +244,8 @@ create_maubot_symlink() {
 print_onboarding() {
     local username="$1"
     local server_ip
-    server_ip=$(hostname -I | awk '{print $1}')
+    # NixOS: use ip command instead of hostname -I
+    server_ip=$(ip -4 addr show scope global | grep -oP '(?<=inet\s)\d+(\.\d+){3}' | head -1)
 
     echo ""
     echo "=========================================="