feat(ui/alerts): register /alerts/* routes with placeholder pages

Adds 6 lazy-loaded route entries for the alerting UI (Inbox, All, History,
Rules list, Rule editor wizard, Silences) plus an `/alerts` → `/alerts/inbox`
redirect. Page components are placeholder stubs to be replaced in Phase 5/6/7.

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

ui/src/pages/Alerts/AllAlertsPage.tsx

@@ -0,0 +1,3 @@
+export default function AllAlertsPage() {
+  return <div>AllAlertsPage — coming soon</div>;
+}

ui/src/pages/Alerts/HistoryPage.tsx

@@ -0,0 +1,3 @@
+export default function HistoryPage() {
+  return <div>HistoryPage — coming soon</div>;
+}

ui/src/pages/Alerts/InboxPage.tsx

@@ -0,0 +1,3 @@
+export default function InboxPage() {
+  return <div>InboxPage — coming soon</div>;
+}

ui/src/pages/Alerts/RuleEditor/RuleEditorWizard.tsx

@@ -0,0 +1,3 @@
+export default function RuleEditorWizard() {
+  return <div>RuleEditorWizard — coming soon</div>;
+}

ui/src/pages/Alerts/RulesListPage.tsx

@@ -0,0 +1,3 @@
+export default function RulesListPage() {
+  return <div>RulesListPage — coming soon</div>;
+}

ui/src/pages/Alerts/SilencesPage.tsx

@@ -0,0 +1,3 @@
+export default function SilencesPage() {
+  return <div>SilencesPage — coming soon</div>;
+}

ui/src/router.tsx

@@ -23,6 +23,12 @@ const OutboundConnectionEditor = lazy(() => import('./pages/Admin/OutboundConnec
 const SensitiveKeysPage = lazy(() => import('./pages/Admin/SensitiveKeysPage'));
 const AppsTab = lazy(() => import('./pages/AppsTab/AppsTab'));
 const SwaggerPage = lazy(() => import('./pages/Swagger/SwaggerPage'));
+const InboxPage        = lazy(() => import('./pages/Alerts/InboxPage'));
+const AllAlertsPage    = lazy(() => import('./pages/Alerts/AllAlertsPage'));
+const HistoryPage      = lazy(() => import('./pages/Alerts/HistoryPage'));
+const RulesListPage    = lazy(() => import('./pages/Alerts/RulesListPage'));
+const RuleEditorWizard = lazy(() => import('./pages/Alerts/RuleEditor/RuleEditorWizard'));
+const SilencesPage     = lazy(() => import('./pages/Alerts/SilencesPage'));
 
 function SuspenseWrapper({ children }: { children: React.ReactNode }) {
   return (
@@ -75,6 +81,16 @@ export const router = createBrowserRouter([
           { path: 'apps/new', element: <SuspenseWrapper><AppsTab /></SuspenseWrapper> },
           { path: 'apps/:appId', element: <SuspenseWrapper><AppsTab /></SuspenseWrapper> },
 
+          // Alerts
+          { path: 'alerts', element: <Navigate to="/alerts/inbox" replace /> },
+          { path: 'alerts/inbox',     element: <SuspenseWrapper><InboxPage /></SuspenseWrapper> },
+          { path: 'alerts/all',       element: <SuspenseWrapper><AllAlertsPage /></SuspenseWrapper> },
+          { path: 'alerts/history',   element: <SuspenseWrapper><HistoryPage /></SuspenseWrapper> },
+          { path: 'alerts/rules',     element: <SuspenseWrapper><RulesListPage /></SuspenseWrapper> },
+          { path: 'alerts/rules/new', element: <SuspenseWrapper><RuleEditorWizard /></SuspenseWrapper> },
+          { path: 'alerts/rules/:id', element: <SuspenseWrapper><RuleEditorWizard /></SuspenseWrapper> },
+          { path: 'alerts/silences',  element: <SuspenseWrapper><SilencesPage /></SuspenseWrapper> },
+
           // Admin (ADMIN role required)
           {
             element: <RequireAdmin />,