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/pages/Exchanges/ExchangeList.module.css

@@ -1,74 +0,0 @@
-.list {
-  display: flex;
-  flex-direction: column;
-  overflow-y: auto;
-  height: 100%;
-  border-right: 1px solid var(--border);
-  background: var(--surface);
-}
-
-.item {
-  display: flex;
-  align-items: center;
-  gap: 0.5rem;
-  padding: 0.625rem 0.75rem;
-  cursor: pointer;
-  border-bottom: 1px solid var(--border-light);
-  font-size: 0.8125rem;
-  transition: background 0.1s;
-}
-
-.item:hover {
-  background: var(--surface-hover);
-}
-
-.itemSelected {
-  background: var(--surface-active);
-  border-left: 3px solid var(--amber);
-  padding-left: calc(0.75rem - 3px);
-}
-
-.dot {
-  width: 8px;
-  height: 8px;
-  border-radius: 50%;
-  flex-shrink: 0;
-}
-
-.dotOk { background: var(--success); }
-.dotErr { background: var(--error); }
-.dotRun { background: var(--running); }
-
-.meta {
-  flex: 1;
-  min-width: 0;
-}
-
-.exchangeId {
-  font-family: var(--font-mono);
-  font-size: 0.6875rem;
-  color: var(--text-muted);
-  overflow: hidden;
-  text-overflow: ellipsis;
-  white-space: nowrap;
-}
-
-.duration {
-  font-family: var(--font-mono);
-  font-size: 0.75rem;
-  color: var(--text-secondary);
-  flex-shrink: 0;
-}
-
-.timestamp {
-  font-size: 0.6875rem;
-  color: var(--text-muted);
-  flex-shrink: 0;
-}
-
-.empty {
-  padding: 2rem;
-  text-align: center;
-  color: var(--text-muted);
-  font-size: 0.8125rem;
-}

ui/src/pages/Exchanges/ExchangeList.tsx

@@ -1,56 +0,0 @@
-import type { ExecutionSummary } from '../../api/types';
-import styles from './ExchangeList.module.css';
-
-interface ExchangeListProps {
-  exchanges: ExecutionSummary[];
-  selectedId?: string;
-  onSelect: (exchange: ExecutionSummary) => void;
-}
-
-function formatDuration(ms: number): string {
-  if (ms >= 60_000) return `${(ms / 1000).toFixed(0)}s`;
-  if (ms >= 1000) return `${(ms / 1000).toFixed(2)}s`;
-  return `${ms}ms`;
-}
-
-function formatTime(iso: string): string {
-  const d = new Date(iso);
-  const h = String(d.getHours()).padStart(2, '0');
-  const m = String(d.getMinutes()).padStart(2, '0');
-  const s = String(d.getSeconds()).padStart(2, '0');
-  return `${h}:${m}:${s}`;
-}
-
-function dotClass(status: string): string {
-  switch (status) {
-    case 'COMPLETED': return styles.dotOk;
-    case 'FAILED': return styles.dotErr;
-    case 'RUNNING': return styles.dotRun;
-    default: return styles.dotOk;
-  }
-}
-
-export function ExchangeList({ exchanges, selectedId, onSelect }: ExchangeListProps) {
-  if (exchanges.length === 0) {
-    return <div className={styles.empty}>No exchanges found</div>;
-  }
-
-  return (
-    <div className={styles.list}>
-      {exchanges.map((ex) => (
-        <div
-          key={ex.executionId}
-          className={`${styles.item} ${selectedId === ex.executionId ? styles.itemSelected : ''}`}
-          onClick={() => onSelect(ex)}
-        >
-          <span className={`${styles.dot} ${dotClass(ex.status)}`} />
-          <div className={styles.meta}>
-            <div className={styles.exchangeId}>{ex.executionId.slice(0, 12)}</div>
-          </div>
-          <span className={styles.duration}>{formatDuration(ex.durationMs)}</span>
-          <span className={styles.timestamp}>{formatTime(ex.startTime)}</span>
-        </div>
-      ))}
-    </div>
-  );
-}