feat(channel): 同步 vivid 最新渠道设计 — 手动全量同步端点/并发0=不限/同名别名报错

对齐 vivid 6039423/5802749/a1f808f/cfb6d49/aba8474/b01636f:
- 新增 POST /channels/sync-models:已保存渠道手动全量同步,上游不可达/
  空清单直接报错(保存路径仍降级为告警);渠道行按钮不再弹勾选框,
  表单内对已保存渠道同样直同步,新渠道保持预览+勾选即绑定
- 渠道并发 0 = 不限制(原 0=默认5),上限放开到 int32,槽位 Lua 本就
  max=0 放行
- 别名与上游模型同名提交即报错「留空即同名」,前后端双校验
- 渠道列表去掉上游地址与模型两列(同 vivid),状态徽章悬浮显示失败原因

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

backend/internal/http/router/router.go

@@ -146,6 +146,7 @@ func New(cfg *config.Config, auth *service.AuthService, handlers Handlers) *gin.
 		authed.POST("/channels", handlers.ChannelAdmin.Save)
 		authed.POST("/channels/delete", handlers.ChannelAdmin.Delete)
 		authed.POST("/channels/fetch-models", handlers.ChannelAdmin.FetchModels)
+		authed.POST("/channels/sync-models", handlers.ChannelAdmin.SyncModels)
 		authed.POST("/channels/import-models", handlers.ChannelAdmin.ImportModels)
 		authed.POST("/channels/unbind-model", handlers.ChannelAdmin.UnbindModel)
 		authed.GET("/providers", handlers.AdminRead.Providers)