enhance(dev): make heap snapshot downloadable

.github/workflows/get-backend-memory.yml

@@ -96,6 +96,13 @@ jobs:
         MK_MEMORY_COMPARE_WARMUP_ROUNDS: 1
         MK_MEMORY_HEAP_SNAPSHOT: 1
       run: node head/.github/scripts/measure-backend-memory-comparison.mts base head memory-base.json memory-head.json
+    - name: Upload head heap snapshot
+      uses: actions/upload-artifact@v7
+      with:
+        name: backend-memory-head-heap-snapshot
+        path: head-heap-snapshot.heapsnapshot
+        if-no-files-found: error
+        retention-days: 7
     - name: Measure backend loaded JS footprint
       run: |
         node head/.github/scripts/backend-js-footprint.mjs base js-footprint-base.json