fix(phpstan): remove stale Flash::add() baseline suppression

Security module now calls Flash::add() directly (for 'warning' type),
so PHPStan no longer reports it as unused — the baseline entry became unmatched.

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

phpstan-baseline.neon

@@ -1374,12 +1374,6 @@ parameters:
 			count: 1
 			path: core/Service/User/UserTenantContextService.php
 
-		-
-			message: '#^Public method "MintyPHP\\Support\\Flash\:\:add\(\)" is never used$#'
-			identifier: public.method.unused
-			count: 1
-			path: core/Support/Flash.php
-
 		-
 			message: '#^Public method "MintyPHP\\Support\\Flash\:\:dismissByKey\(\)" is never used$#'
 			identifier: public.method.unused