fix: 出勤率改为当天计算（当天出勤数/总运营数）

之前用近30天activeDays/totalDays计算，现改为：
当天里程>0的车辆数 / 部门总运营车辆数 × 100%

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

src/server/routes/vehicles.ts

@@ -693,23 +693,20 @@ app.get('/dept-stats', async (c) => {
     mgrMap.get(mgr)!.push(v);
   }
 
-  // Compute attendance & mileage for a set of vehicles
+  // Compute attendance (today) & avg mileage (30d) for a set of vehicles
   const getMileageStats = (vList: Vehicle[]) => {
-    let totalActive = 0;
-    let totalDays = 0;
+    const todayActive = vList.filter((v) => (todayMileageMap.get(v.plateNumber) || 0) > 0).length;
     let totalMileage = 0;
     let count = 0;
     for (const v of vList) {
       const m = mileageMap.get(v.plateNumber);
       if (m) {
-        totalActive += m.activeDays;
-        totalDays += m.totalDays;
         totalMileage += m.avgMileage;
         count++;
       }
     }
     return {
-      attendanceRate: totalDays > 0 ? Math.round((totalActive / totalDays) * 1000) / 10 : 0,
+      attendanceRate: vList.length > 0 ? Math.round((todayActive / vList.length) * 1000) / 10 : 0,
       avgMileage: count > 0 ? Math.round(totalMileage / count) : 0,
     };
   };