Fix CI: replace heredoc with echo for YAML compatibility

Heredoc REPORTEOF was indented inside YAML run block, preventing
shell from recognizing the terminator.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: highimpact-dev

.github/workflows/skill-shield-ci.yml

@@ -131,9 +131,7 @@ $FINDINGS_LIST
           done
 
           # Write report for next step
-          cat > /tmp/scan-report.txt << REPORTEOF
-$REPORT
-REPORTEOF
+          echo "$REPORT" > /tmp/scan-report.txt
           echo "overall_pass=$OVERALL_PASS" >> $GITHUB_OUTPUT
           echo "lowest_score=$LOWEST_SCORE" >> $GITHUB_OUTPUT