Add user/share management integration tests
Integration Tests:
- test_user_workflow: Create, update, reset password, delete user
- test_multiple_users: Create multiple users, verify list, cleanup
- test_user_permissions: Admin vs regular user permissions
Test Features:
- Unique usernames (timestamp-based) to avoid conflicts
- Using existing data/auth.sqlite database
- Cleanup after each test
- Password verification
- Permission checking
Test Coverage:
- create_user() + bcrypt password hashing
- get_user() + user data verification
- check_password() + correct/wrong password tests
- update_user() + home_dir, uid, permissions update
- reset_password() + password change verification
- list_users() + multiple users list
- delete_user() + cleanup verification
Build: ✅ markbase-core
Tests: 3 passed, 0 failed
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