Implement role and user management enhancements

- Added MaxIpLimit to roles, allowing for the configuration of simultaneous IP limits for users.
- Updated role creation and update commands to include MaxIpLimit, ensuring proper handling in the application logic.
- Enhanced user management by introducing a DELETE endpoint for user accounts, with appropriate checks to prevent self-deletion.
- Updated documentation to reflect changes in role and user management, clarifying the new IP limit functionality and user deletion process.
- Adjusted related tests to cover new functionality and ensure robust validation of role and user management features.

.env.example

@@ -29,6 +29,8 @@ AdminSeed__Password=change-me-strong-admin-password
 # ── Роли по умолчанию ─────────────────────────────────────────────────────
 # Квота конфигов для системной роли "user" (выдаётся при регистрации).
 Roles__DefaultUserMaxConfigs=3
+# Лимит одновременных IP на клиента (limitIp в 3x-ui) для системной роли "user"; -1 = без лимита.
+Roles__DefaultUserMaxIpLimit=2
 
 # ── Rate limiting ────────────────────────────────────────────────────────
 # Лимит запросов/мин на auth-эндпоинты (login/register/refresh/telegram/subscription). По умолчанию 20.