feat(api): delete workspace groups and record who signed a content event

server/src/WebDrop.Core/ChannelWorkspace.cs

@@ -84,6 +84,13 @@ public sealed partial class ChannelService
     public WorkspaceState CreateWorkspaceGroup(Id16 id, Credentials creds, string name) => CreateWorkspaceGroupResult(id, creds, name).State;
     public WorkspaceState RenameWorkspaceGroup(Id16 id, Credentials creds, string groupId, string name) => ChangeWorkspace(id, creds, (_, state, _) =>
         (state.Groups.Find(g => g.Id == groupId) ?? throw new WebDropException(ErrorCode.NotFound)).Name = WorkspaceName(name));
+    /// <summary>删除分组:组里的频道回到未分组,频道本身和内容都不动</summary>
+    public WorkspaceState DeleteWorkspaceGroup(Id16 id, Credentials creds, string groupId) => ChangeWorkspace(id, creds, (_, state, _) =>
+    {
+        var group = state.Groups.Find(g => g.Id == groupId) ?? throw new WebDropException(ErrorCode.NotFound);
+        foreach (var channel in state.Channels.Where(c => c.GroupId == groupId)) channel.GroupId = null;
+        state.Groups.Remove(group);
+    });
     public WorkspaceState CreateWorkspaceFolder(Id16 id, Credentials creds, string threadId, string? parentId, string name) => ChangeWorkspace(id, creds, (_, state, _) =>
         state.Folders.Add(new WorkspaceFolder { Id = Guid.NewGuid().ToString(), ThreadId = threadId, ParentId = parentId, Name = WorkspaceName(name) }));
     public WorkspaceState RenameWorkspaceFolder(Id16 id, Credentials creds, string folderId, string name) => ChangeWorkspace(id, creds, (_, state, _) =>