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/Support/DatabaseSessionRepositoryInterface.php

@@ -2,6 +2,7 @@
 
 namespace MintyPHP\Repository\Support;
 
+/** Contract for database-level session control: advisory locks and transaction management. */
 interface DatabaseSessionRepositoryInterface
 {
     public function acquireAdvisoryLock(string $lockName, int $timeoutSeconds = 0): bool;
@@ -13,4 +14,11 @@ interface DatabaseSessionRepositoryInterface
     public function commitTransaction(): void;
 
     public function rollbackTransaction(): void;
+
+    /**
+     * @template T
+     * @param callable(): T $callback
+     * @return T
+     */
+    public function transaction(callable $callback): mixed;
 }