chore(ui): remove dead code from navigation redesign

Deleted:
- ScopeTrail component (replaced by inline breadcrumb in TopBar)
- ExchangeList component (replaced by Dashboard DataTable)
- ExchangeDetail page (replaced by inline split view)

Removed from Dashboard:
- flattenProcessors() function (unused after detail panel removal)
- 11 dead CSS classes (panelSection, overviewGrid, errorBlock,
  inspectLink, openDetailLink, filterBar, etc.)

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

ui/src/components/ScopeTrail.module.css

@@ -1,40 +0,0 @@
-.trail {
-  display: flex;
-  align-items: center;
-  gap: 0;
-  font-size: 0.8125rem;
-  color: var(--text-muted);
-  min-height: 1.5rem;
-}
-
-.segment {
-  display: inline-flex;
-  align-items: center;
-}
-
-.link {
-  color: var(--text-secondary);
-  text-decoration: none;
-  cursor: pointer;
-  background: none;
-  border: none;
-  padding: 0;
-  font: inherit;
-  font-size: 0.8125rem;
-}
-
-.link:hover {
-  color: var(--amber);
-  text-decoration: underline;
-}
-
-.separator {
-  margin: 0 0.375rem;
-  color: var(--text-muted);
-  user-select: none;
-}
-
-.current {
-  color: var(--text-primary);
-  font-weight: 500;
-}

ui/src/components/ScopeTrail.tsx

@@ -1,38 +0,0 @@
-import type { Scope } from '../hooks/useScope';
-import styles from './ScopeTrail.module.css';
-
-interface ScopeTrailProps {
-  scope: Scope;
-  onNavigate: (path: string) => void;
-}
-
-export function ScopeTrail({ scope, onNavigate }: ScopeTrailProps) {
-  const segments: { label: string; path: string }[] = [
-    { label: 'All Applications', path: `/${scope.tab}` },
-  ];
-
-  if (scope.appId) {
-    segments.push({ label: scope.appId, path: `/${scope.tab}/${scope.appId}` });
-  }
-
-  if (scope.routeId) {
-    segments.push({ label: scope.routeId, path: `/${scope.tab}/${scope.appId}/${scope.routeId}` });
-  }
-
-  return (
-    <nav className={styles.trail}>
-      {segments.map((seg, i) => (
-        <span key={seg.path} className={styles.segment}>
-          {i > 0 && <span className={styles.separator}>&gt;</span>}
-          {i < segments.length - 1 ? (
-            <button className={styles.link} onClick={() => onNavigate(seg.path)}>
-              {seg.label}
-            </button>
-          ) : (
-            <span className={styles.current}>{seg.label}</span>
-          )}
-        </span>
-      ))}
-    </nav>
-  );
-}