fix: expand env vars and check absolute paths in build_reference_tree

The build_reference_tree() function was prepending config_dir to all
'into' paths without expanding environment variables or checking if the
result was absolute. This caused paths like /workspace/ai//workspace/ComfyUI
instead of /workspace/ComfyUI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

artifact_git_download.sh

@@ -724,8 +724,17 @@ build_reference_tree() {
     # Determine installation directory
     local lib_dir
     if [[ -n "$into" ]]; then
-      local config_dir=$(dirname "$(realpath "${effective_config}")")
-      lib_dir="$config_dir/$into"
+      # Expand environment variables
+      local expanded_into
+      expanded_into=$(expand_env_vars "$into" 2>/dev/null) || expanded_into="$into"
+
+      # Check if expanded path is absolute
+      if [[ "$expanded_into" == /* ]]; then
+        lib_dir="$expanded_into"
+      else
+        local config_dir=$(dirname "$(realpath "${effective_config}")")
+        lib_dir="$config_dir/$expanded_into"
+      fi
     else
       lib_dir="$ARTY_LIBS_DIR/$lib_name"
     fi