Give the operator a provider-health readout

The per-user retry ledger has recorded every AI delivery outcome for a
long time, but no surface ever read it for the operator: a central
provider could fail on every call for weeks and the admin console said
nothing. The AI settings section now carries a health card, backed by a
new admin-only endpoint that folds the ledger into one row per provider
type: users tracked, users currently failing, the worst uninterrupted
failure run, and the last success and failure instants. Operator-managed
types sort first because their failure takes the shared fallback down
for everyone whose chain relies on it. Counts and timestamps only; the
response never names a user.

src/app/admin/[section]/renderer.tsx

@@ -18,6 +18,7 @@ import { useAuth } from "@/hooks/use-auth";
 import { AboutSection } from "@/components/settings/about-section";
 import { AiQualitySection } from "@/components/admin/ai-quality-section";
 import { AiServerKeySection } from "@/components/admin/ai-server-key-section";
+import { ProviderHealthSection } from "@/components/admin/provider-health-section";
 import { CentralCodexSection } from "@/components/admin/central-codex-section";
 import { AssistantSection } from "@/components/admin/assistant-section";
 import { CoachFeedbackSection } from "@/components/admin/coach-feedback-section";
@@ -89,6 +90,7 @@ export function AdminSectionRenderer({
           <AssistantSection />
           <AiServerKeySection />
           <CentralCodexSection />
+          <ProviderHealthSection />
           <CoachFeedbackSection />
           <AiQualitySection />
         </SectionFrame>