fix: 里程环比改为真实值（与前一天对比）

- 后端缓存刷新时查询前一天总里程（yesterdayTotal）
- 前端计算真实环比：(今日-昨日)/昨日*100%
- 上涨显示蓝色↑，下跌显示红色↓
- 昨日无数据时不显示环比

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

src/modules/mileage/MonitoringView.tsx

@@ -106,7 +106,7 @@ export default function MonitoringView() {
   const [appliedMileageRange, setAppliedMileageRange] = useState({ min: '', max: '' });
 
   const [vehicles, setVehicles] = useState<MonitoringVehicle[]>([]);
-  const [stats, setStats] = useState<MonitoringStats>({ totalToday: 0, totalAll: 0, vehicleCount: 0 });
+  const [stats, setStats] = useState<MonitoringStats>({ totalToday: 0, totalAll: 0, vehicleCount: 0, yesterdayTotal: 0 });
   const [filterOptions, setFilterOptions] = useState<MonitoringFilters>({ departments: [], customers: [], plates: [], projects: [], entities: [] });
   const [total, setTotal] = useState(0);
   const [page, setPage] = useState(1);
@@ -713,7 +713,11 @@ export default function MonitoringView() {
           </div>
           <div className="text-2xl font-black tracking-tighter flex items-baseline gap-1">
             {Math.round(sortBy === 'today' ? stats.totalToday : stats.totalAll).toLocaleString()}
-            {sortBy === 'today' && <span className="text-blue-400 text-[10px] font-bold">{'\u2191'}12%</span>}
+            {sortBy === 'today' && stats.yesterdayTotal > 0 && (() => {
+              const change = ((stats.totalToday - stats.yesterdayTotal) / stats.yesterdayTotal) * 100;
+              const isUp = change >= 0;
+              return <span className={`text-[10px] font-bold ${isUp ? 'text-blue-400' : 'text-rose-400'}`}>{isUp ? '\u2191' : '\u2193'}{Math.abs(change).toFixed(1)}%</span>;
+            })()}
           </div>
           <div className="absolute -right-4 -bottom-4 w-12 h-12 bg-blue-500/10 rounded-full blur-xl"></div>
         </div>