fix(clickhouse): harden R/W path P0–P3 (cleanup, durability, rollups)

Honest TTL cleanup semantics; enqueue-safe dedup with flush retry and writer
metrics; model insert hooks; latest-per-node and hourly metric/openresty
rollups; small-host pool/async defaults, traffic hourly TTL, and UV labeling.

frontend/app/(main)/components/dashboard/stat-cards.tsx

@@ -34,7 +34,7 @@ export function DashboardStatCards({
             {formatCompactNumber(traffic.request_count)}
           </div>
           <p className="text-[10px] text-muted-foreground">
-            独立访客 {formatCompactNumber(traffic.unique_visitors)} · 错误{' '}
+            窗口UV(估) {formatCompactNumber(traffic.unique_visitors)} · 错误{' '}
             {formatCompactNumber(traffic.error_count)} · 估算 QPS{' '}
             {traffic.estimated_qps.toFixed(2)}
           </p>

frontend/app/(main)/nodes/components/node-observability.tsx

@@ -661,7 +661,7 @@ export function NodeObservability({
                     </p>
                     <p className="mt-2 text-sm text-muted-foreground">
                       {trafficSummary
-                        ? `近 60 秒 · UV ${formatMetricCount(trafficSummary.unique_visitor_count)}`
+                        ? `近 60 秒 · 窗口UV ${formatMetricCount(trafficSummary.unique_visitor_count)}`
                         : '暂无窗口流量摘要'}
                     </p>
                   </div>