Enhance eMMC provisioning dashboard: add backups directory information to API response, update UI to include a refresh button for saved backups, and improve user instructions for setting golden images.

chromium-setup/emmc-provisioning/dashboard/app.py

@@ -332,7 +332,7 @@ def api_backup_upload():
 
 @app.route("/api/backups")
 def api_backups():
-    return jsonify({"backups": list_backups()})
+    return jsonify({"backups": list_backups(), "backups_dir": str(BACKUPS_DIR)})
 
 
 @app.route("/api/backups/<path:name>/set-as-golden", methods=["POST"])