渠道: 分协议 Base URL + 模型抽屉/远程拉取/操作图标

- 渠道支持分协议 base_url(chat/responses/messages 各一), 网关按协议选 base 直通
  (如智谱三种格式不同 base, 一个渠道即可), UpstreamURL 按 proto 拼接
- 渠道模型改为下方抽屉: 当前绑定列表(内联改上游/解除)、从接口拉取(remote 预览+勾选添加)、手动添加
- 新增 /channels/:id/models/remote 预览接口; 操作按钮加 Phosphor 图标
- 修复 formats jsonb 更新未序列化问题; 手机端渠道卡片化

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

server/internal/api/router.go

@@ -104,6 +104,7 @@ func NewRouter(a *app.App, gw *proxy.Gateway) *gin.Engine {
 			admin.DELETE("/channels/:id", h.AdminDeleteChannel)
 			admin.POST("/channels/:id/test", h.AdminTestChannel)
 			admin.POST("/channels/:id/models/import", h.AdminImportChannelModels)
+			admin.GET("/channels/:id/models/remote", h.AdminChannelRemoteModels)
 			admin.GET("/channels/:id/models", h.AdminChannelModels)
 			admin.POST("/channels/:id/models", h.AdminChannelAddModel)
 			admin.PATCH("/channels/:id/models/:bid", h.AdminChannelUpdateModel)