refactor(client): centralize error feedback with toast events

- emit API/network failures through a shared toast event bridge

- remove per-page inline error notifications to avoid duplicate error UI

- dedupe repeated toast messages to keep feedback readable

client/src/pages/environment/EnvironmentsPage.tsx

@@ -171,7 +171,6 @@ export function EnvironmentsPage() {
           </Button>
         </div>
       </div>
-      {error && <p className={styles.error}>{error}</p>}
       {loading ? (
         <p className={styles.muted}>{t('environments.loading')}</p>
       ) : (