Fix TYPE-MISMATCH issues in email diagnostic scripts

modules/email/email-diagnostics.sh:
- Quote account_found variable in comparisons (lines 374, 378)

modules/email/deliverability-test.sh:
- Quote listed variable in comparison (line 166)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

modules/email/deliverability-test.sh

@@ -163,7 +163,7 @@ else
         fi
     done
 
-    if [ $listed -gt 0 ]; then
+    if [ "$listed" -gt 0 ]; then
         echo ""
         print_warning "  ⚠ Your IP is listed on $listed blacklist(s)"
         echo "    Recommendation: Use blacklist-check tool for delisting options"