Fix silent exit due to arithmetic expression with set -e

((processed_count++)) returns exit code 1 when count is 0, causing
silent termination with set -e. Use assignment form instead.

Co-Authored-By: Claude (global.anthropic.claude-opus-4-5-20251101-v1:0) <noreply@anthropic.com>

Author: JackStrohm-asana

stage_for_s3.bash

@@ -119,7 +119,7 @@ for file in *.tar.xz; do
       echo "✓ Done: Archive now contains:"
       tar -tf "$new_name" | head
       echo ""
-      ((processed_count++))
+      processed_count=$((processed_count + 1))
     else
       echo "Warning: Skipped $new_name due to unexpected filename format."
     fi