refactor: consolidate breadcrumbs to single TopBar instance

Remove duplicate in-page breadcrumbs (ExchangeDetail, AgentHealth scope
trail) and improve the global TopBar breadcrumb with semantic labels and
a context-based override for pages with richer navigation data.

- Add BreadcrumbProvider from design system v0.1.12
- LayoutShell: label map prettifies URL segments (apps→Applications, etc.)
- ExchangeDetail: uses useBreadcrumb() to set semantic trail via context
- AgentHealth: remove scope trail, keep live-count badge standalone

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

ui/src/pages/AgentHealth/AgentHealth.tsx

@@ -1,5 +1,5 @@
 import { useState, useMemo } from 'react';
-import { useParams, Link } from 'react-router';
+import { useParams } from 'react-router';
 import {
   StatCard, StatusDot, Badge, MonoText, ProgressBar,
   GroupCard, DataTable, LineChart, EventFeed, DetailPanel,
@@ -463,15 +463,7 @@ export default function AgentHealth() {
         />
       </div>
 
-      {/* Scope trail + badges */}
-      <div className={styles.scopeTrail}>
-        {appId && (
-          <>
-            <Link to="/agents" className={styles.scopeLink}>All Agents</Link>
-            <span className={styles.scopeSep}>&#9656;</span>
-            <span className={styles.scopeCurrent}>{appId}</span>
-          </>
-        )}
+      <div style={{ marginBottom: 12 }}>
         <Badge
           label={`${liveCount}/${totalInstances} live`}
           color={deadCount > 0 ? 'error' : staleCount > 0 ? 'warning' : 'success'}