feat: 通道组并入「添加通道」表单，不再单独新建

- 去掉单独的「新建通道组」入口：添加通道表单的目标可以一次填多个
  （10.0.1.11-13:22、10.0.1.11:8080-8082、逗号分隔），预览每个地址分到的连续端口
- 表单新增「通道组」选项：不分组 / 新建通道组 / 已有组；多个目标自动放进新建的组，
  组名默认与通道名称相同；加入组时名称可不填，按「组名 (主机)」命名
- 闲置关闭、最长时长、限速、访问控制、责任人等设置对每个地址都生效，与单个通道一致
- 编辑通道时可以新建通道组并移入；组卡片上「添加地址」打开同一个表单并选好该组
- 编辑通道组只负责改名、责任人和加入已有通道
- 多个目标的连通性测试并发进行并汇总结果；网页表单补上责任人与限速
- 接口：POST /api/tunnels/batch（dry_run 预览、group_id / new_group），
  PUT /api/tunnels/{id} 支持 new_group；移除 /api/groups/preview 及组接口里的批量建通道

README_EN.md

@@ -58,7 +58,7 @@ PortRelay turns that into three steps:
 - When approval is required, the app shows a system notification and you approve or deny with one click. The requester's page refreshes on its own.
 - **The access clock starts at the first connection**, so a teammate can accept an invite now and use it later.
 - When access expires or is revoked, **existing connections are dropped too**. Unauthorized connections are reset (TCP RST) and logged.
-- **Tunnel groups** open several hosts and ports at once (for example `10.0.1.11-13` × `22, 8080`) on a contiguous block of gateway ports. A group shares one invite link and one set of grants: a teammate is authorized once for the whole group, and one revoke disconnects them everywhere.
+- **Tunnel groups**: the add-tunnel form accepts several targets at once (for example `10.0.1.11-13:22, 10.0.1.11:8080`), creates one tunnel per address on a contiguous block of gateway ports and puts them in one group. A group shares one invite link and one set of grants: a teammate is authorized once for the whole group, and one revoke disconnects them everywhere.
 
 **Tunnel lifecycle**
 
@@ -221,7 +221,7 @@ Open ⚙️ Settings and fill in:
 2. Keep the default access mode, **仅授权链接** (invite-only). Click **邀请** (Invite), then choose how long access lasts, how many devices may use the link, and whether approval is required.
 3. Send the generated message or QR code. Once the teammate has entered their name, they can connect their database client or SSH to `192.168.1.10:33660`.
 
-To open several hosts at once (a set of servers, say), click **新建通道组** (New tunnel group), enter hosts `10.0.1.11-13` and ports `22`, check the previewed port mapping and create it, then click **邀请整组** (Invite group). Existing tunnels can be ticked to join the group as well.
+To open several hosts at once (a set of servers, say), use the same **添加通道** (Add tunnel) form and enter `10.0.1.11-13:22` as the target. The form previews the port mapping and selects 新建通道组 (New tunnel group); idle close, bandwidth and access settings apply to every address. Then click **邀请整组** (Invite group). To add addresses later, click **添加地址** (Add address) on the group card; an existing tunnel can join a group from its edit form.
 
 ## Configuration