fix(ui): use describeApiError across remaining error-surface sites

Extends the previous describeApiError rollout to the rest of the UI.
Two symptom classes covered:

 - Bare e.message / err.message in toast descriptions would render
   "undefined" on Spring error bodies (plain objects without a proper
   Error prototype). Affected: OidcConfigPage (save/test/delete),
   ClaimMappingRulesModal (save + test), AgentHealth (dismiss),
   RouteControlBar (route action + replay).

 - Inline {String(error)} on load-failure banners would render
   "[object Object]". Affected: InboxPage, RulesListPage, SilencesPage,
   OutboundConnectionsPage.

Not touched: auth-store, AppsTab, UsersTab — they already guard with
`e instanceof Error` and fall back to a static string; replacing the
fallback with describeApiError would be a behavioral change best
evaluated separately.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Exchanges/RouteControlBar.tsx

@@ -4,6 +4,7 @@ import { useToast, ConfirmDialog } from '@cameleer/design-system';
 import { useSendRouteCommand, useReplayExchange } from '../../api/queries/commands';
 import type { CommandGroupResponse } from '../../api/queries/commands';
 import { useEnvironmentStore } from '../../api/environment-store';
+import { describeApiError } from '../../api/errors';
 import styles from './RouteControlBar.module.css';
 
 interface RouteControlBarProps {
@@ -68,7 +69,7 @@ export function RouteControlBar({ application, routeId, routeState, hasRouteCont
           setSendingAction(null);
         },
         onError: (err) => {
-          toast({ title: `Route ${action} failed`, description: err.message, variant: 'error', duration: 86_400_000 });
+          toast({ title: `Route ${action} failed`, description: describeApiError(err), variant: 'error', duration: 86_400_000 });
           setSendingAction(null);
         },
       },
@@ -92,7 +93,7 @@ export function RouteControlBar({ application, routeId, routeState, hasRouteCont
           setSendingAction(null);
         },
         onError: (err) => {
-          toast({ title: 'Replay failed', description: err.message, variant: 'error', duration: 86_400_000 });
+          toast({ title: 'Replay failed', description: describeApiError(err), variant: 'error', duration: 86_400_000 });
           setSendingAction(null);
         },
       },