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.module.css

@@ -31,35 +31,6 @@
 .routesWarning { color: var(--warning); }
 .routesError { color: var(--error); }
 
-/* Scope breadcrumb trail */
-.scopeTrail {
-  display: flex;
-  align-items: center;
-  gap: 6px;
-  margin-bottom: 12px;
-  font-size: 12px;
-}
-
-.scopeLink {
-  color: var(--amber);
-  text-decoration: none;
-  font-weight: 500;
-}
-
-.scopeLink:hover {
-  text-decoration: underline;
-}
-
-.scopeSep {
-  color: var(--text-muted);
-  font-size: 10px;
-}
-
-.scopeCurrent {
-  color: var(--text-primary);
-  font-weight: 600;
-  font-family: var(--font-mono);
-}
 
 /* Section header */
 .sectionTitle {