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/Scheduler/SchedulerRuntimeRepository.php

@@ -5,6 +5,7 @@ namespace MintyPHP\Repository\Scheduler;
 use MintyPHP\DB;
 use MintyPHP\Domain\Taxonomy\SchedulerRuntimeResult;
 
+/** Tracks scheduler daemon heartbeat, result codes, and error state. */
 class SchedulerRuntimeRepository implements SchedulerRuntimeRepositoryInterface
 {
     public function touchHeartbeat(string $result, ?string $errorCode = null, ?string $heartbeatAtUtc = null): bool