fix: dismiss stale session-timeout flash on auto-login, resolve PHPStan and i18n issues

- Add Flash::dismissByKey() to clear flash messages by key+scope
- Dismiss 'session_timeout' flash after successful remember-me auto-login
  so the message doesn't persist through manual logout
- Suppress PHPStan false positives for dynamically defined MINTY_ALLOW_OUTPUT
- Remove unnecessary ?? [] fallbacks on preg_match_all results in tests
- Add missing i18n key 'No active roles are configured yet.'

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

i18n/default_de.json

@@ -159,6 +159,7 @@
   "Select permissions": "Berechtigungen auswählen",
   "No permissions available": "Keine Berechtigungen verfügbar",
   "No active permissions are configured yet.": "Es sind noch keine aktiven Berechtigungen konfiguriert.",
+  "No active roles are configured yet.": "Es sind noch keine aktiven Rollen konfiguriert.",
   "Permission denied": "Keine Berechtigung",
   "No active tenant assigned": "Kein aktiver Mandant zugewiesen",
   "Please select at least one tenant": "Bitte mindestens einen Mandanten auswählen",

i18n/default_en.json

@@ -159,6 +159,7 @@
   "Select permissions": "Select permissions",
   "No permissions available": "No permissions available",
   "No active permissions are configured yet.": "No active permissions are configured yet.",
+  "No active roles are configured yet.": "No active roles are configured yet.",
   "Permission denied": "Permission denied",
   "No active tenant assigned": "No active tenant assigned",
   "Please select at least one tenant": "Please select at least one tenant",