refactor: move Dashboard to /apps, add Metrics sidebar entry, scope by app

- Route / redirects to /apps, Dashboard serves both /apps and /apps/:id
- When appId is present, exchanges/routes/agents/search are scoped to that app
- Remove Dashboards sidebar link, add Metrics link
- Sidebar section labels (Applications, Agents) are now clickable nav links
  with separate chevron for collapse toggle
- Update all breadcrumbs from Dashboard/href:'/' to Applications/href:'/apps'
- Remove AppDetail page (replaced by scoped Dashboard)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/pages/ExchangeDetail/ExchangeDetail.tsx

@@ -117,7 +117,7 @@ export function ExchangeDetail() {
       >
         <TopBar
           breadcrumb={[
-            { label: 'Dashboard', href: '/' },
+            { label: 'Applications', href: '/apps' },
             { label: 'Exchanges' },
             { label: id ?? 'Unknown' },
           ]}
@@ -144,7 +144,7 @@ export function ExchangeDetail() {
       {/* Top bar */}
       <TopBar
         breadcrumb={[
-          { label: 'Dashboard', href: '/' },
+          { label: 'Applications', href: '/apps' },
           { label: exchange.route, href: `/routes/${exchange.route}` },
           { label: exchange.id },
         ]}