Make the terminal work offline end to end, and add stock screens

Terminal (PRD 5.3/5.5):
- Opens with no network: a service worker caches the app shell and build
  assets, and the last confirmed session and product list are kept on the
  phone. Only a definitive 401/403 sends the cashier to the login page.
- The offline queue is keyed by cashier and branch, sends only the
  signed-in cashier's sales, chunks to the server's batch limit, and acts
  on the per-sale result: synced, or rejected with the reason shown and
  never retried. Rows from the old queue are adopted on first sync.
- Several products per sale (tap to add), optional customer details, and
  a printable receipt. The banner shows sales waiting to sync and any
  that need attention; sign-out warns about unsynced sales.
- M-Pesa only appears when FEATURE_MPESA is on. A timed-out prompt now
  tells the cashier not to take cash until the payment is checked,
  instead of reporting it as failed.

Admin:
- New Stock page: stock per branch with low/out flags, physical counts
  and adjustments, inter-branch transfers, morning dispatch and evening
  count entry, and recent movements.
- Dashboard shows stock on hand per branch and links to Stock.
- Staff page can deactivate and reactivate accounts.
- Products page is read-only for branch managers and edits the low-stock
  alert level.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/admin/dashboard/page.tsx

@@ -5,7 +5,7 @@ import { useRouter } from "next/navigation";
 import Link from "next/link";
 import { apiFetch, ApiError } from "@/lib/api";
 import { useTransactionFeed } from "@/lib/pollingFeed";
-import { AuthUser, Branch, DashboardSummary, ReconciliationRow } from "@/lib/types";
+import { AuthUser, Branch, DashboardSummary, ReconciliationRow, StockLevel } from "@/lib/types";
 import { useToast } from "@/components/ui/Toast";
 import { SkeletonCardGrid, SkeletonTable } from "@/components/ui/Skeleton";
 import EmptyState from "@/components/ui/EmptyState";
@@ -16,6 +16,7 @@ import LiveStatsRow from "@/components/admin/LiveStatsRow";
 import BranchRankingList from "@/components/admin/BranchRankingList";
 import ActivityFeedMatrix from "@/components/admin/ActivityFeedMatrix";
 import ReconciliationGrid from "@/components/admin/ReconciliationGrid";
+import StockSummaryCard from "@/components/admin/StockSummaryCard";
 
 export default function AdminDashboardPage() {
   const router = useRouter();
@@ -27,6 +28,7 @@ export default function AdminDashboardPage() {
   const [selectedBranchId, setSelectedBranchId] = useState<string>("ALL");
   const [summary, setSummary] = useState<DashboardSummary | null>(null);
   const [reconciliation, setReconciliation] = useState<ReconciliationRow[]>([]);
+  const [stock, setStock] = useState<StockLevel[]>([]);
   const [loading, setLoading] = useState(true);
 
   const { events: feedTransactions, connected } = useTransactionFeed(selectedBranchId, 50);
@@ -75,12 +77,14 @@ export default function AdminDashboardPage() {
     setLoading(true);
     try {
       const branchParam = selectedBranchId === "ALL" ? "" : "?branchId=" + selectedBranchId;
-      const [summaryRes, reconRes] = await Promise.all([
+      const [summaryRes, reconRes, stockRes] = await Promise.all([
         apiFetch<DashboardSummary>("/api/dashboard/summary" + branchParam),
         apiFetch<{ rows: ReconciliationRow[] }>("/api/dashboard/reconciliation" + branchParam),
+        apiFetch<{ levels: StockLevel[] }>("/api/stock" + branchParam),
       ]);
       setSummary(summaryRes);
       setReconciliation(reconRes.rows);
+      setStock(stockRes.levels);
     } catch (err) {
       show(err instanceof ApiError ? err.message : "Could not load dashboard data", "error");
     }
@@ -138,6 +142,9 @@ export default function AdminDashboardPage() {
                 Platform
               </Link>
             )}
+            <Link href="/admin/stock" className="tap-target flex items-center rounded-xl2 bg-white/10 px-4 text-sm font-medium text-white hover:bg-white/15">
+              Stock
+            </Link>
             <Link href="/admin/products" className="tap-target flex items-center rounded-xl2 bg-white/10 px-4 text-sm font-medium text-white hover:bg-white/15">
               Sizes
             </Link>
@@ -183,6 +190,8 @@ export default function AdminDashboardPage() {
               pendingMpesa={summary.totals.pendingMpesa}
             />
 
+            <StockSummaryCard levels={stock} />
+
             <div className="grid grid-cols-1 gap-3 sm:grid-cols-2">
               <PaymentSplitDonut cashTotal={summary.totals.cashTotal} mpesaTotal={summary.totals.mpesaTotal} />
               <LiveStatsRow