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/AgentHealth/AgentHealth.tsx

@@ -100,7 +100,7 @@ function buildTrendData(agent: AgentHealthData) {
 
 function buildBreadcrumb(scope: Scope) {
   const crumbs: { label: string; href?: string }[] = [
-    { label: 'System', href: '/' },
+    { label: 'Applications', href: '/apps' },
     { label: 'Agents', href: '/agents' },
   ]
   if (scope.level === 'app' || scope.level === 'instance') {