UX 审查收尾：AI 解读过渡标记 + 极端温度视觉强化

P2-17：AI 快速判断→完整解读过渡标记
- AiEvidencePanel 新增 useTransitionMarker hook
- AI 从 loading→ready 后显示"✓ Updated/已更新"徽标（4 秒后消失）
- 绿色动画徽标 fadeUpIn，避免用户以为信息没变

P2-18：极端温度视觉强化
- globals.css 新增 temp-extreme-hot（橙红辉光 ≥40°C/≥104°F）
- globals.css 新增 temp-extreme-cold（冰蓝辉光 ≤-5°C/≤23°F）
- PanelSections Hero 温度值自动应用极端温度样式

Tested: npx tsc --noEmit

frontend/components/dashboard/ScanTerminalCard.module.css

@@ -1027,6 +1027,18 @@
   color: var(--color-accent-primary);
 }
 
+.root :global(.scan-ai-updated-badge) {
+  display: inline-block;
+  padding: 2px 8px;
+  border-radius: 999px;
+  background: rgba(34, 197, 94, 0.12);
+  color: #4ade80;
+  font-size: 10px;
+  font-weight: 700;
+  margin-bottom: 6px;
+  animation: fadeUpIn 0.3s ease;
+}
+
 .root :global(.scan-ai-raw-metar) {
   margin-top: 12px;
   padding-top: 12px;

frontend/components/dashboard/scan-terminal/AiEvidencePanel.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import { useEffect, useState } from "react";
 import type {
   AiCityForecastPayload,
   AiCityForecastState,
@@ -13,6 +14,18 @@ function confidenceBadge(confidence: string | null, isEn: boolean) {
   return { label: isEn ? "Low" : "低", tone: "low" };
 }
 
+function useTransitionMarker(status: string, hasContent: boolean) {
+  const [showUpdated, setShowUpdated] = useState(false);
+  useEffect(() => {
+    if (status === "ready" && hasContent) {
+      setShowUpdated(true);
+      const id = setTimeout(() => setShowUpdated(false), 4000);
+      return () => clearTimeout(id);
+    }
+  }, [status, hasContent]);
+  return showUpdated;
+}
+
 export function AiEvidencePanel({
   aiBullets,
   aiCityForecast,
@@ -62,6 +75,8 @@ export function AiEvidencePanel({
       ? `${formatTemperatureValue(aiRangeLow, tempSymbol, { digits: 0 })} ~ ${formatTemperatureValue(aiRangeHigh, tempSymbol, { digits: 0 })}`
       : null;
 
+  const showUpdatedBadge = useTransitionMarker(aiForecast.status, Boolean(aiCityForecast));
+
   return (
     <section className="scan-ai-city-section scan-ai-city-ai-read">
       <div className="scan-ai-city-section-title">
@@ -143,6 +158,11 @@ export function AiEvidencePanel({
             </>
           ) : aiForecast.status === "ready" && aiCityForecast ? (
             <>
+              {showUpdatedBadge ? (
+                <span className="scan-ai-updated-badge">
+                  {isEn ? "✓ Updated" : "✓ 已更新"}
+                </span>
+              ) : null}
               <p className="scan-ai-weather-summary">
                 {aiRuleEvidenceMode ? aiRuleEvidenceText : aiReadCompleteText}
               </p>