feat(dashboard): 最近请求缓存命中列 + 中文模式人民币计价 + 价格解析记忆化

- 最近请求表新增缓存命中率列（缓存读取/总输入）
- useCurrency：中文界面费用按最新 USD→CNY 汇率显示 ¥，英文保持 $（open.er-api.com，缓存 12h，失败兜底 7.2）
- match_price 记忆化缓存：O(记录数×5910) → O(模型种类×5910)，扫描从秒级降到百毫秒级
- 仪表盘右上角显示加载耗时/数据量（get_summary 往返埋点）；Rust 侧分段计时

src/hooks/useCurrency.ts

@@ -0,0 +1,83 @@
+import { useCallback, useEffect, useState } from "react";
+import { useTranslation } from "../i18n";
+import { fmtUsd } from "../lib/dashboard-format";
+
+/**
+ * USD → CNY exchange rate for the dashboard.
+ * Chinese mode shows prices in CNY (latest available rate), English stays in
+ * USD. The rate is fetched once and cached in localStorage for 12h; any
+ * failure falls back to a conservative fixed rate so the UI never blocks.
+ */
+
+const FALLBACK_RATE = 7.2;
+const CACHE_KEY = "kimi-switch-cny-rate";
+const CACHE_TTL = 12 * 60 * 60 * 1000; // 12 hours
+
+function readCachedRate(): number | null {
+  try {
+    const raw = localStorage.getItem(CACHE_KEY);
+    if (!raw) return null;
+    const { ts, rate } = JSON.parse(raw) as { ts: number; rate: number };
+    if (Date.now() - ts > CACHE_TTL || !(rate > 1)) return null;
+    return rate;
+  } catch {
+    return null;
+  }
+}
+
+function writeCachedRate(rate: number) {
+  try {
+    localStorage.setItem(CACHE_KEY, JSON.stringify({ ts: Date.now(), rate }));
+  } catch {
+    /* ignore */
+  }
+}
+
+export function useCurrency() {
+  const { lang } = useTranslation();
+  const [rate, setRate] = useState<number | null>(null);
+
+  useEffect(() => {
+    let cancelled = false;
+    (async () => {
+      const cached = readCachedRate();
+      if (cached) {
+        setRate(cached);
+        return;
+      }
+      try {
+        const res = await fetch("https://open.er-api.com/v6/latest/USD");
+        if (res.ok) {
+          const data = (await res.json()) as { rates?: { CNY?: number } };
+          const cny = Number(data.rates?.CNY);
+          if (cny > 1) {
+            if (!cancelled) setRate(cny);
+            writeCachedRate(cny);
+            return;
+          }
+        }
+      } catch {
+        /* network blocked → fallback */
+      }
+      if (!cancelled) setRate(FALLBACK_RATE);
+    })();
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  /** Format a USD cost for display: CNY in Chinese mode, USD otherwise. */
+  const money = useCallback(
+    (usd: number): string => {
+      if (lang !== "zh") return fmtUsd(usd);
+      const v = (Number(usd) || 0) * (rate ?? FALLBACK_RATE);
+      if (v === 0) return "¥0.00";
+      if (v < 0.1) return "¥" + v.toFixed(3);
+      if (v < 1) return "¥" + v.toFixed(2);
+      return "¥" + v.toFixed(2);
+    },
+    [lang, rate],
+  );
+
+  return { money, cnyRate: rate ?? FALLBACK_RATE };
+}

src/hooks/useDashboard.ts

@@ -22,16 +22,23 @@ export function useDashboard() {
   const [data, setData] = useState<SummaryResult | null>(null);
   const [loading, setLoading] = useState(false);
   const [error, setError] = useState<string | null>(null);
+  /** Round-trip timing for the last get_summary call (user-perceived lag). */
+  const [loadStats, setLoadStats] = useState<{ ms: number; kb: number } | null>(null);
 
   const refresh = useCallback(async (force = false) => {
     setLoading(true);
     setError(null);
+    const start = performance.now();
     try {
       const result = await invoke<SummaryResult>("get_summary", {
         range,
         refresh: force,
       });
       setData(result);
+      setLoadStats({
+        ms: Math.round(performance.now() - start),
+        kb: Math.round(JSON.stringify(result).length / 1024),
+      });
     } catch (err) {
       const msg = err instanceof Error ? err.message : String(err);
       setError(msg);
@@ -53,5 +60,5 @@ export function useDashboard() {
     }
   }, []);
 
-  return { range, changeRange, data, loading, error, refresh };
+  return { range, changeRange, data, loading, error, refresh, loadStats };
 }