feat(i18n): translate TimingTab + TimingWaterfall + add common.understand (R4 #1, #3)

Round-3 F-I18N covered ConversationTab, StatsTab, StatsCharts, and labels in
TimingWaterfall, but missed:

 - TimingTab.tsx — 5 user-visible labels (Timestamp, Method, Status, Request
   size, Response size) were hardcoded English.
 - TimingWaterfall.tsx — empty state ("No timing data available.") and Total
   latency label were also hardcoded.
 - common.understand — RiskNoticeModal calls
   `useTranslations("common")("understand")` but the key did not exist;
   only the `|| "I understand"` fallback rescued it, leaving pt-BR users
   seeing English.

Adds the missing 7 trafficInspector.timing* keys and common.understand to both
en.json and pt-BR.json, wires `useTranslations` in both components, and adds a
source-grep test asserting no English literals remain in JSX and that all 8
keys exist in both locales.

src/app/(dashboard)/dashboard/tools/traffic-inspector/components/shared/TimingWaterfall.tsx

@@ -13,7 +13,7 @@ export function TimingWaterfall({ request }: TimingWaterfallProps) {
   const total = totalLatencyMs ?? (proxyLatencyMs ?? 0) + (upstreamLatencyMs ?? 0);
 
   if (!total) {
-    return <p className="text-sm text-text-muted">No timing data available.</p>;
+    return <p className="text-sm text-text-muted">{t("timingNoData")}</p>;
   }
 
   const segments: Array<{ label: string; ms: number; color: string }> = [
@@ -51,7 +51,7 @@ export function TimingWaterfall({ request }: TimingWaterfallProps) {
         })}
       </div>
       <div className="flex justify-between text-xs font-medium text-text-main border-t border-border pt-2">
-        <span>Total latency</span>
+        <span>{t("timingTotalLatency")}</span>
         <span>{total}ms</span>
       </div>
     </div>

src/app/(dashboard)/dashboard/tools/traffic-inspector/components/tabs/TimingTab.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import { useTranslations } from "next-intl";
 import type { InterceptedRequest } from "@/mitm/inspector/types";
 import { TimingWaterfall } from "../shared/TimingWaterfall";
 
@@ -8,28 +9,29 @@ interface TimingTabProps {
 }
 
 export function TimingTab({ request }: TimingTabProps) {
+  const t = useTranslations("trafficInspector");
   return (
     <div className="p-4 h-full overflow-auto space-y-4">
       <TimingWaterfall request={request} />
       <div className="border-t border-border pt-3 space-y-1 text-xs text-text-muted">
         <div className="flex justify-between">
-          <span>Timestamp</span>
+          <span>{t("timingTimestamp")}</span>
           <span className="font-mono">{request.timestamp}</span>
         </div>
         <div className="flex justify-between">
-          <span>Method</span>
+          <span>{t("timingMethod")}</span>
           <span className="font-mono">{request.method}</span>
         </div>
         <div className="flex justify-between">
-          <span>Status</span>
+          <span>{t("timingStatus")}</span>
           <span className="font-mono">{String(request.status)}</span>
         </div>
         <div className="flex justify-between">
-          <span>Request size</span>
+          <span>{t("timingRequestSize")}</span>
           <span className="font-mono">{request.requestSize} B</span>
         </div>
         <div className="flex justify-between">
-          <span>Response size</span>
+          <span>{t("timingResponseSize")}</span>
           <span className="font-mono">{request.responseSize} B</span>
         </div>
       </div>

src/i18n/messages/en.json

@@ -2,6 +2,7 @@
   "common": {
     "save": "Save",
     "cancel": "Cancel",
+    "understand": "I understand",
     "delete": "Delete",
     "loading": "Loading...",
     "error": "An error occurred",
@@ -7480,6 +7481,13 @@
     "statsSuccessful": "Successful",
     "statsTotalRequests": "Total requests",
     "timingProxyOverhead": "Proxy overhead",
-    "timingUpstreamResponse": "Upstream response"
+    "timingUpstreamResponse": "Upstream response",
+    "timingNoData": "No timing data available.",
+    "timingTotalLatency": "Total latency",
+    "timingTimestamp": "Timestamp",
+    "timingMethod": "Method",
+    "timingStatus": "Status",
+    "timingRequestSize": "Request size",
+    "timingResponseSize": "Response size"
   }
 }

src/i18n/messages/pt-BR.json

@@ -2,6 +2,7 @@
   "common": {
     "save": "Salvar",
     "cancel": "Cancelar",
+    "understand": "Eu entendo",
     "delete": "Excluir",
     "loading": "Carregando...",
     "error": "Ocorreu um erro",
@@ -7470,6 +7471,13 @@
     "statsSuccessful": "Bem-sucedidas",
     "statsTotalRequests": "Total de requisições",
     "timingProxyOverhead": "Overhead do proxy",
-    "timingUpstreamResponse": "Resposta upstream"
+    "timingUpstreamResponse": "Resposta upstream",
+    "timingNoData": "Nenhum dado de tempo disponível.",
+    "timingTotalLatency": "Latência total",
+    "timingTimestamp": "Timestamp",
+    "timingMethod": "Método",
+    "timingStatus": "Status",
+    "timingRequestSize": "Tamanho da requisição",
+    "timingResponseSize": "Tamanho da resposta"
   }
 }

tests/unit/ui/timing-i18n.test.tsx

@@ -0,0 +1,73 @@
+/**
+ * i18n coverage for TimingTab + TimingWaterfall (R4 fix #3).
+ * Source-text inspection — no JSDOM render needed.
+ *
+ * Round-3 F-I18N translated ConversationTab/StatsTab/StatsCharts but missed
+ * TimingTab (5 labels) and TimingWaterfall (2 labels). Round-4 closed the gap.
+ */
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import path from "node:path";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+const TIMING_TAB = path.resolve(
+  __dirname,
+  "../../../src/app/(dashboard)/dashboard/tools/traffic-inspector/components/tabs/TimingTab.tsx",
+);
+const TIMING_WATERFALL = path.resolve(
+  __dirname,
+  "../../../src/app/(dashboard)/dashboard/tools/traffic-inspector/components/shared/TimingWaterfall.tsx",
+);
+const EN = path.resolve(__dirname, "../../../src/i18n/messages/en.json");
+const PT = path.resolve(__dirname, "../../../src/i18n/messages/pt-BR.json");
+
+const tabSrc = readFileSync(TIMING_TAB, "utf-8");
+const waterfallSrc = readFileSync(TIMING_WATERFALL, "utf-8");
+const en = JSON.parse(readFileSync(EN, "utf-8"));
+const pt = JSON.parse(readFileSync(PT, "utf-8"));
+
+describe("Timing i18n (R4 fix #3)", () => {
+  it("TimingTab uses useTranslations and has no hardcoded English labels", () => {
+    assert.ok(tabSrc.includes('useTranslations("trafficInspector")'));
+    for (const lit of ["Timestamp", "Method", "Status", "Request size", "Response size"]) {
+      assert.ok(
+        !new RegExp(`<span[^>]*>${lit}</span>`).test(tabSrc),
+        `TimingTab must not render hardcoded "${lit}" — use t() instead`,
+      );
+    }
+    for (const key of ["timingTimestamp", "timingMethod", "timingStatus", "timingRequestSize", "timingResponseSize"]) {
+      assert.ok(tabSrc.includes(`t("${key}")`), `TimingTab must call t("${key}")`);
+    }
+  });
+
+  it("TimingWaterfall translates the empty state and total latency label", () => {
+    assert.ok(!waterfallSrc.includes("No timing data available."));
+    assert.ok(!waterfallSrc.includes(">Total latency<"));
+    assert.ok(waterfallSrc.includes('t("timingNoData")'));
+    assert.ok(waterfallSrc.includes('t("timingTotalLatency")'));
+  });
+
+  it("All 7 new timing keys exist in both en.json and pt-BR.json", () => {
+    const keys = [
+      "timingNoData",
+      "timingTotalLatency",
+      "timingTimestamp",
+      "timingMethod",
+      "timingStatus",
+      "timingRequestSize",
+      "timingResponseSize",
+    ];
+    for (const k of keys) {
+      assert.ok(en.trafficInspector?.[k], `en.json must have trafficInspector.${k}`);
+      assert.ok(pt.trafficInspector?.[k], `pt-BR.json must have trafficInspector.${k}`);
+    }
+  });
+
+  it("common.understand is present in both locales (RiskNoticeModal namespace)", () => {
+    assert.equal(en.common?.understand, "I understand");
+    assert.equal(pt.common?.understand, "Eu entendo");
+  });
+});