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/Org/DepartmentRepository.php

@@ -6,6 +6,7 @@ use MintyPHP\DB;
 use MintyPHP\Repository\Support\RepoQuery;
 use MintyPHP\Repository\Support\RepositoryArrayHelper;
 
+/** Reads and writes department records with cost center, code tracking, and pagination. */
 class DepartmentRepository implements DepartmentRepositoryInterface
 {
     public function list(): array