fix: sidebar route selection and missing routes after server restart

Two sidebar bugs fixed:

1. Route entries never highlighted on navigation because sidebar-utils
   generated /apps/ paths for route children while effectiveSelectedPath
   normalizes to /exchanges/. The design system does exact string matching.

2. Routes disappeared from sidebar when agents had no recent exchange
   data. Heartbeat carried routeStates (with route IDs as keys) but
   AgentRegistryService.heartbeat() never updated AgentInfo.routeIds.
   After server restart, auto-heal registered agents with empty routes,
   leaving ClickHouse (24h window) as the only discovery source.

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

ui/src/components/sidebar-utils.ts

@@ -89,7 +89,7 @@ export function buildAppTreeNodes(
       badge: r.routeState
         ? `${r.routeState.toUpperCase()} \u00b7 ${formatCount(r.exchangeCount)}`
         : formatCount(r.exchangeCount),
-      path: `/apps/${app.id}/${r.id}`,
+      path: `/exchanges/${app.id}/${r.id}`,
       starrable: true,
       starKey: `route:${app.id}/${r.id}`,
     })),