feat(frontend): 100% backend API coverage — 7 batches

Batch A: Fix Breadcrumbs (usePathname), rewrite ComplianceTab (DataTable+FilterBar+ColumnToggle), delete dead code (a11yAudit.js, policyEngine.js), wire toast notifications (Combos, Providers)
Batch B: ModelAvailabilityPanel — cooldown badges, clear action, auto-refresh
Batch C: BudgetTab — spend cards, progress bars, budget limits form
Batch D: FallbackChainsEditor — color-coded provider chains, create/delete
Batch E: PoliciesPanel — circuit breaker states, locked identifiers, force unlock
Batch F: EvalsTab — expandable suites, run eval, DataTable results
Batch G: TokenHealthBadge + /api/token-health — OAuth health in header

8 new files, 9 modified, 2 deleted. Build passes (exit 0).

src/shared/components/Header.js

@@ -5,6 +5,7 @@ import Link from "next/link";
 import Image from "next/image";
 import PropTypes from "prop-types";
 import { ThemeToggle } from "@/shared/components";
+import TokenHealthBadge from "./TokenHealthBadge";
 import {
   OAUTH_PROVIDERS,
   APIKEY_PROVIDERS,
@@ -170,6 +171,9 @@ export default function Header({ onMenuClick, showMenuButton = true }) {
         {/* Theme toggle */}
         <ThemeToggle />
 
+        {/* Token health */}
+        <TokenHealthBadge />
+
         {/* Logout button */}
         <button
           onClick={handleLogout}