refactor(jpush): move vendor field handling into ThirdPartyChannel struct

Move the vendor switch logic into the ThirdPartyChannel struct as Set/IsEmpty/Normalize
methods to improve encapsulation and eliminate code duplication in the vendor params
builder. Also simplify messageToParams to reuse buildMessagePayload results and remove
unused notification_type extras from push notifications.

internal/pkg/jpush/vendor/params.go

@@ -120,32 +120,11 @@ func (f *Factory) Build(params MessageParams, cfg config.ChannelConfig) *PushPay
 		if m == nil {
 			continue
 		}
-		switch c.VendorName() {
-		case "xiaomi":
-			tpc.Xiaomi = m
-		case "huawei":
-			tpc.Huawei = m
-		case "oppo":
-			tpc.OPPO = m
-		case "vivo":
-			tpc.VIVO = m
-		case "meizu":
-			tpc.Meizu = m
-		case "honor":
-			tpc.Honor = m
-		case "fcm":
-			tpc.FCM = m
-		}
-	}
-
-	// 全部厂商字段为空则置 nil，避免序列化出空的 third_party_channel
-	if tpc.Xiaomi == nil && tpc.Huawei == nil && tpc.OPPO == nil &&
-		tpc.VIVO == nil && tpc.Meizu == nil && tpc.Honor == nil && tpc.FCM == nil {
-		tpc = nil
+		tpc.Set(c.VendorName(), m)
 	}
 
 	return &PushPayload{
 		Notification: notification,
-		TPC:          tpc,
+		TPC:          tpc.Normalize(),
 	}
 }