Add comprehensive security tests for authentication, roles, and user management

- Enhance `test-auth.sh` with SQL injection, XSS, and credential validation tests.
- Extend `test-roles-permissions.sh` to include unauthorized access and duplicate role creation tests.
- Improve `test-users.sh` with checks for invalid emails, duplicate users, and unauthorized actions.
- Introduce `test-security.sh` for thorough security assessments including CSRF, SQL injection, XSS, rate limiting, and session management.
- Add `.serena.gitignore` and `.serena/project.yml` for project configuration and file management.

.serena/.gitignore

@@ -0,0 +1 @@
+/cache