docs: add class docblocks, business-rule comments, and transaction wrapper

- Add single-line class docblocks to all 59 repository classes and interfaces
  describing scope and responsibility
- Add multi-line docblocks to key services documenting business rules:
  AuthService (6-step login cascade), ImportService (3-phase CSV workflow),
  TenantScopeService (strict/permissive modes), PermissionService (RBAC
  resolution + two-tier caching), UserAccountService (atomicity + audit)
- Add transaction(callable) wrapper to DatabaseSessionRepository to DRY up
  begin/commit/rollback boilerplate

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/Repository/Tenant/UserTenantRepositoryInterface.php

@@ -2,6 +2,7 @@
 
 namespace MintyPHP\Repository\Tenant;
 
+/** Contract for querying user-tenant membership and per-tenant user counts. */
 interface UserTenantRepositoryInterface
 {
     public function listTenantIdsByUserId(int $userId): array;