fix: Planner 从多单元凑弹药，不再被单个 TotalMunitions 卡死

每个威胁可从多个火力单元汇集弹药，直到满足需求或耗尽。
单元测试 24/24 通过。

src/CounterDrone.Core/Algorithms/DefaultDefensePlanner.cs

@@ -113,45 +113,64 @@ namespace CounterDrone.Core.Algorithms
                     continue;
                 }
 
-                // 选最早可拦截的
-                var best = candidates
-                    .OrderBy(c => c.EarliestInterceptTime)
-                    .ThenByDescending(c => c.KillProbability)
-                    .First();
+                // 计算总弹药需求
+                var neededAmmo = MatchAmmo((PowerType)threat.Target.PowerType);
+                var ammo = _ammoCatalog.FirstOrDefault(a => a.AerosolType == (int)neededAmmo);
+                int totalRoundsNeeded = CalcRoundsNeeded(threat, ammo, env,
+                    candidates[0].Unit.Type == PlatformType.AirBased);
 
-                var ammo = _ammoCatalog.FirstOrDefault(a => a.AerosolType == (int)best.AmmoType);
-                int roundsNeeded = CalcRoundsNeeded(threat, ammo, env, best.Unit.Type == PlatformType.AirBased);
-                int actualRounds = Math.Min(roundsNeeded, remainingMunitions[best.Unit.Id]);
+                // 从多个候选单元凑弹药，直到满足需求或耗尽
+                int roundsCollected = 0;
+                var assignedUnits = new List<(FireUnit unit, int rounds, List<FireEvent> events)>();
 
-                if (actualRounds <= 0) { plan.ThreatsUnengaged++; continue; }
-
-                var fireEvents = GenerateFireEvents(threat, best.Unit, best.AmmoType,
-                    actualRounds, ammo, env);
-
-                plan.Assignments.Add(new UnitAssignment
+                foreach (var c in candidates.OrderBy(c => c.EarliestInterceptTime)
+                    .ThenByDescending(c => c.KillProbability))
                 {
-                    FireUnitId = best.Unit.Id,
-                    DroneGroupId = threat.GroupId,
-                    AmmoType = best.AmmoType,
-                    RoundsFired = actualRounds,
-                    FirstFireTime = fireEvents.Count > 0 ? fireEvents[0].FireTime : 0,
-                    FireEvents = fireEvents,
-                });
+                    if (roundsCollected >= totalRoundsNeeded) break;
+                    int remaining = remainingMunitions.GetValueOrDefault(c.Unit.Id, 0);
+                    if (remaining <= 0) continue;
+
+                    int toTake = Math.Min(remaining, totalRoundsNeeded - roundsCollected);
+                    var fireEvents = GenerateFireEvents(threat, c.Unit, c.AmmoType, toTake, ammo, env);
+                    assignedUnits.Add((c.Unit, toTake, fireEvents));
+                    remainingMunitions[c.Unit.Id] -= toTake;
+                    roundsCollected += toTake;
+                }
+
+                if (roundsCollected <= 0) { plan.ThreatsUnengaged++; continue; }
+
+                foreach (var (unit, rounds, fireEvents) in assignedUnits)
+                {
+                    plan.Assignments.Add(new UnitAssignment
+                    {
+                        FireUnitId = unit.Id,
+                        DroneGroupId = threat.GroupId,
+                        AmmoType = neededAmmo,
+                        RoundsFired = rounds,
+                        FirstFireTime = fireEvents.Count > 0 ? fireEvents[0].FireTime : 0,
+                        FireEvents = fireEvents,
+                    });
+                    plan.MergedSchedule.AddRange(fireEvents);
+                }
 
-                plan.MergedSchedule.AddRange(fireEvents);
-                remainingMunitions[best.Unit.Id] -= actualRounds;
                 plan.ThreatsEngaged++;
             }
 
             plan.MergedSchedule.Sort((a, b) => a.FireTime.CompareTo(b.FireTime));
-            plan.OverallProbability = plan.Assignments.Count > 0
-                ? (float)plan.Assignments.Average(a =>
-                {
-                    var t = sortedThreats.First(th => th.GroupId == a.DroneGroupId);
-                    var a2 = _ammoCatalog.FirstOrDefault(s => s.AerosolType == (int)a.AmmoType);
-                    return ComputeInterceptProbability(t, a2, a.RoundsFired, env);
-                })
-                : 0f;
+
+            // 按威胁汇总概率
+            var threatProbs = new List<float>();
+            foreach (var threat in sortedThreats)
+            {
+                var a2 = _ammoCatalog.FirstOrDefault(s =>
+                    s.AerosolType == (int)MatchAmmo((PowerType)threat.Target.PowerType));
+                int totalRounds = plan.Assignments
+                    .Where(a => a.DroneGroupId == threat.GroupId)
+                    .Sum(a => a.RoundsFired);
+                if (totalRounds > 0)
+                    threatProbs.Add(ComputeInterceptProbability(threat, a2, totalRounds, env));
+            }
+            plan.OverallProbability = threatProbs.Count > 0 ? threatProbs.Average() : 0f;
             plan.Summary = plan.ThreatsEngaged > 0
                 ? $"分配 {plan.ThreatsEngaged} 个威胁，{plan.ThreatsUnengaged} 个无方案"
                 : "无威胁被分配拦截方案";