Set draft status for multimodal MNN learning path

Added draft status to the learning path and updated metadata.

Author: pareenaverma

content/learning-paths/cross-platform/multimodel_mnn_v9/_index.md

@@ -1,6 +1,10 @@
 ---
 title: Build a Multimodal Retail Restocking Assistant on Armv9 With MNN
 
+draft: true
+cascade:
+    draft: true
+    
 minutes_to_complete: 60
 
 who_is_this_for: This learning path is for developers and engineers who want to run multimodal image, audio, and text models on Armv9 Linux systems using MNN as a portable, CPU-first inference runtime. It is aimed at readers who are comfortable building software from source and want a reproducible on-device workflow without quantization or heterogeneous scheduling.