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/run/RunDetailPage.tsx

@@ -213,11 +213,6 @@ export function RunDetailPage() {
         <AutoRefreshIndicator active={polling} pulseKey={pulseKey} error={!!error} onClick={manualRefresh} />
       </div>
 
-      {error && (
-        <Notification variant="error">
-          {error.startsWith('404') ? t('errors.not_found') : error}
-        </Notification>
-      )}
       {loading && <p className={styles.muted}>{t('runs.loading')}</p>}
 
       {run && (