test: add 15 Dart security scanner fixtures

[WNZhao]

Summary

• add 15 inert Dart security-scanner fixtures under vulns/dart/
• cover command/SQL injection, traversal, hard-coded credentials, weak randomness, SSRF, dynamic code loading, temp files, log injection, partial comparison, TLS bypass, redirect, error exposure, permissions, and archive traversal
• refresh generated vulnerability catalogs

Validation

• dart format --output=none --set-exit-if-changed vulns/dart
• dart analyze vulns/dart (No issues found)
• bash scripts/validate-test-case.sh (all 6 groups passed)
• git diff --check

All examples remain unreachable behind NEVER_RUN = false.