feat: add BoundChannelId field to Token model

Add BoundChannelId field to support binding a token to a specific channel.
When set, the token will always use the bound channel for requests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

model/token.go

@@ -27,7 +27,8 @@ type Token struct {
 	AllowIps           *string        `json:"allow_ips" gorm:"default:''"`
 	UsedQuota          int            `json:"used_quota" gorm:"default:0"` // used quota
 	Group              string         `json:"group" gorm:"default:''"`
-	CrossGroupRetry    bool           `json:"cross_group_retry"` // 跨分组重试，仅auto分组有效
+	CrossGroupRetry    bool           `json:"cross_group_retry"`                      // 跨分组重试，仅auto分组有效
+	BoundChannelId     *int           `json:"bound_channel_id" gorm:"index"`          // 绑定的渠道ID，nil表示不绑定
 	DeletedAt          gorm.DeletedAt `gorm:"index"`
 }