fix(scheduling): rescue candidates should be close-to-qualifying, not zero-mileage

For rescue_hopeless (换走) scenario, completely rethought candidate logic:

Before: showed biggest-gap candidates (0 mileage) → pointless, customer can't
  drive them to target
After: prioritize candidates where customer's remaining driving can push them
  over the target line (canQualifyAfterSwap), sorted by smallest gap first

Example: customer drives 178km/day × 57 days = ~1万km remaining.
- 粤AGR6869 (缺口 1990km) → 换后 3.8万, 可达标 ✅ (shown first)
- 浙FF58720 (缺口 6万km) → 换后 1万, 远不达标 (no longer shown first)

Also updated reason text to explain the math:
"该客户剩余57天还能跑约1万km，足以帮缺口小的车冲线"

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

src/modules/scheduling/SuggestionDetail.tsx

@@ -121,7 +121,7 @@ export default function SuggestionDetail({ suggestion: s, onClose, onNotifySucce
             </div>
             <div className="text-[10px] text-slate-400 mb-2.5">
               {isRescue
-                ? '以下车辆里程已充足，可调给当前客户，将此车换走给高里程客户冲刺'
+                ? '以下车辆快达标，换到当前客户处利用剩余天数即可冲线'
                 : '以下车辆里程缺口大，换到该高里程客户处可加速达标'
               }
             </div>

src/server/routes/scheduling/algorithm.ts

@@ -76,26 +76,31 @@ export function generateSuggestions(
   const suggestions: SchedulingSuggestion[] = [];
 
   // --- rescue_hopeless (high priority) ---
-  // For this scenario: take the hopeless car away to a high-mileage customer,
-  // and give the low-mileage customer a replacement from inventory.
-  // Exclude near-qualified candidates (completionRate >= 80%) — no point swapping
-  // in a car that's basically already at target.
-  // Instead, pick cars with BIG gaps: they benefit from any mileage, even at a low customer.
+  // Take the hopeless car away → give to high-mileage customer to sprint.
+  // Replace with an inventory car that is CLOSE to qualifying — the low-mileage
+  // customer's remaining driving days can push it over the finish line.
+  //
+  // Key insight: pick candidates where
+  //   candidate.totalMileage + customer.avgDaily × daysLeft >= yearTarget
+  // i.e., the customer's daily driving is enough to finish the candidate's target.
+  // Among those, prefer the one with the smallest gap (easiest to finish).
+  // Exclude already-qualified (>= 100%) — no value in swapping those.
   for (const vehicle of hopeless) {
+    const customerCanAdd = vehicle.customerAvgDaily * vehicle.daysLeft;
+
     const candidates: CandidateVehicle[] = inventoryVehicles
       .filter((inv) => {
         if (!isTypeCompatible(vehicle.vehicleType, inv.vehicleType)) return false;
         if (inv.region !== vehicle.region) return false;
-        // Exclude near-qualified: yearTarget known and already >= 80% done
+        // Exclude already fully qualified
         const effectiveTarget = inv.yearTarget ?? vehicle.yearTarget;
-        if (effectiveTarget > 0 && inv.totalMileage / effectiveTarget >= 0.8) return false;
+        if (effectiveTarget > 0 && inv.totalMileage >= effectiveTarget) return false;
         return true;
       })
       .map((inv) => {
         const effectiveTarget = inv.yearTarget ?? vehicle.yearTarget;
         const mileageGap = Math.max(0, effectiveTarget - inv.totalMileage);
-        const predictedAfterSwap =
-          inv.totalMileage + vehicle.customerAvgDaily * vehicle.daysLeft;
+        const predictedAfterSwap = inv.totalMileage + customerCanAdd;
         const canQualifyAfterSwap = predictedAfterSwap >= effectiveTarget;
         return {
           plateNumber: inv.plateNumber,
@@ -113,15 +118,20 @@ export function generateSuggestions(
         };
       })
       .sort((a, b) => {
-        // Prefer biggest gap first — these benefit most from any mileage
-        return b.mileageGap - a.mileageGap;
+        // 1. Prefer "can qualify after swap" first
+        if (a.canQualifyAfterSwap !== b.canQualifyAfterSwap)
+          return a.canQualifyAfterSwap ? -1 : 1;
+        // 2. Among qualifiable: smallest gap first (easiest to finish)
+        // Among non-qualifiable: smallest gap first (closest to target)
+        return a.mileageGap - b.mileageGap;
       })
       .slice(0, 5);
 
     const yearRate = vehicle.yearTarget > 0 ? Math.round((vehicle.currentYearMileage / vehicle.yearTarget) * 100) : 0;
     const gap = Math.max(0, vehicle.yearTarget - vehicle.currentYearMileage);
-    const reason = `该车在客户「${vehicle.customer}」处日均仅 ${Math.round(vehicle.customerAvgDaily)} km，本年完成率 ${yearRate}%，还差 ${fmtKmSimple(gap)} km 达标，按当前速度年底无法完成。`
-      + `\n建议：将此车调配给高里程客户冲刺达标，同时从库存调一辆已达标的车给当前客户。`;
+    const canAddKm = Math.round(customerCanAdd);
+    const reason = `该车在客户「${vehicle.customer}」处日均仅 ${Math.round(vehicle.customerAvgDaily)} km，完成率 ${yearRate}%，还差 ${fmtKmSimple(gap)} km，年底无法达标。`
+      + `\n建议：将此车换走给高里程客户冲刺，换上一辆快达标的车——该客户剩余 ${vehicle.daysLeft} 天还能跑约 ${fmtKmSimple(canAddKm)} km，足以帮缺口小的车冲线。`;
 
     suggestions.push({
       id: `hopeless-${vehicle.plateNumber}`,