fix(security): escape LIKE pattern wildcards in admin user search and courses (#533)

[lmduy2612]

Summary

Closes #533.

Prevents SQL/ORM wildcard injection in ilike queries by introducing a shared escapeLikePattern utility and applying it to admin user search (AdminUsersService.listUsers) and course search (CourseService.listCourses).

Changes Made

• Added escapeLikePattern helper in src/utils/sanitize.ts to escape %, _, and \ special characters.
• Applied escapeLikePattern to search queries in src/modules/admin/admin-users.service.ts for users.stellarAddress and users.displayName.
• Standardized src/modules/courses/course.service.ts to use escapeLikePattern.
• Added unit tests in tests/unit/utils/sanitize.test.ts verifying escaping behavior for wildcards and preservation of standard alphanumeric strings (11/11 tests passing).

Acceptance Criteria

• Escape LIKE pattern characters in admin user search
• Apply the same fix to ilike queries across the codebase
• Add a shared utility function for LIKE pattern escaping