新增车辆表及OTA权限与逻辑优化

新增车辆任务与报警表，完善实体与DbContext配置。细化OTA权限校验，增强回传会话IP安全。优化OTA上传与设置面板，调度器支持重启恢复。报警采集逻辑支持历史分段。

MiGu.Server/Fleet/AlarmCollector.cs

@@ -168,29 +168,36 @@ public sealed class AlarmCollector
         var activeByCar = new Dictionary<int, VehicleAlarmRecord>();
         foreach (var a in active) activeByCar[a.CarId] = a; // 每车取一条 active
 
-        // 出现 / 更新
+        // 出现 / 更新：文案或级别变化时先 clear 旧记录再开新 active，保留分段历史
         foreach (var cur in current.Values)
         {
             if (activeByCar.TryGetValue(cur.CarId, out var rec))
             {
-                rec.Info = cur.Info;
-                rec.Level = cur.Level;
-                rec.CarName = cur.CarName;
-                rec.LastAt = now;
-            }
-            else
-            {
-                db.VehicleAlarms.Add(new VehicleAlarmRecord
+                var same =
+                    string.Equals(rec.Info, cur.Info, StringComparison.Ordinal) &&
+                    rec.Level == cur.Level;
+                if (same)
                 {
-                    CarId = cur.CarId,
-                    CarName = cur.CarName,
-                    Info = cur.Info,
-                    Level = cur.Level,
-                    Status = "active",
-                    FirstAt = now,
-                    LastAt = now
-                });
+                    rec.CarName = cur.CarName;
+                    rec.LastAt = now;
+                    continue;
+                }
+
+                rec.Status = "cleared";
+                rec.ResolvedAt = now;
+                rec.DurationSecs = (long)Math.Max(0, (now - rec.FirstAt).TotalSeconds);
             }
+
+            db.VehicleAlarms.Add(new VehicleAlarmRecord
+            {
+                CarId = cur.CarId,
+                CarName = cur.CarName,
+                Info = cur.Info,
+                Level = cur.Level,
+                Status = "active",
+                FirstAt = now,
+                LastAt = now
+            });
         }
 
         // 消失 → 恢复