feat(sp6): /inbox route + sidebar nav link

src/App.tsx

@@ -11,6 +11,7 @@ import { ReconciliationPage } from "@/pages/Reconciliation";
 import { Acks } from "@/pages/Acks";
 import { Batches } from "@/pages/Batches";
 import { BatchDiff } from "@/pages/BatchDiff";
+import Inbox from "@/pages/Inbox";
 
 function NotFound() {
   return (
@@ -33,6 +34,7 @@ export default function App() {
           <Route path="activity" element={<ActivityLog />} />
           <Route path="upload" element={<Upload />} />
           <Route path="reconciliation" element={<ReconciliationPage />} />
+          <Route path="inbox" element={<Inbox />} />
           <Route path="acks" element={<Acks />} />
           <Route path="batches" element={<Batches />} />
           <Route path="batch-diff" element={<BatchDiff />} />