fix: correct response field mappings and add logout button

- SearchResult uses 'data' not 'items', 'total' not 'totalCount'
- ExecutionStats uses 'p99LatencyMs' not 'p99DurationMs'
- TimeseriesBucket uses 'time' not 'timestamp'
- Add user Dropdown with logout action to LayoutShell

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

ui/src/pages/Routes/RoutesMetrics.tsx

@@ -81,7 +81,7 @@ export default function RoutesMetrics() {
       <div style={{ display: 'flex', gap: '1rem', marginBottom: '1.5rem', flexWrap: 'wrap' }}>
         <StatCard label="Total Throughput" value={stats?.totalCount ?? 0} sparkline={sparklineData} />
         <StatCard label="Error Rate" value={stats?.totalCount ? `${(((stats.failedCount ?? 0) / stats.totalCount) * 100).toFixed(1)}%` : '0%'} accent="error" />
-        <StatCard label="P99 Latency" value={`${stats?.p99DurationMs ?? 0}ms`} accent="warning" />
+        <StatCard label="P99 Latency" value={`${stats?.p99LatencyMs ?? 0}ms`} accent="warning" />
         <StatCard label="Success Rate" value={stats?.totalCount ? `${(((stats.totalCount - (stats.failedCount ?? 0)) / stats.totalCount) * 100).toFixed(1)}%` : '100%'} accent="success" />
       </div>