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/snippet/SnippetsPage.tsx

@@ -132,7 +132,6 @@ export function SnippetsPage() {
         </div>
       </div>
 
-      {error && <p className={styles.error}>{error}</p>}
       {loading && <p className={styles.muted}>{t('snippets.loading')}</p>}
 
       {!loading && (