Research limiting creation / editing of projects to "project leads"

Currently, anyone can create a project or add themselves to it (I think there's a related issue for this).

Thoughts:

* Can we take advantage of an existing account level?
* We can have an extremely loose standard on what a project lead is

該 issue 未列出任何檔案、測試或進入點；請先找出現有的專案建立、成員管理與編輯流程，並檢視其中提到的帳戶等級。釐清哪些角色可以執行各項操作，接著將已達成共識的權限規則記錄下來並進行測試，作為 Definition of Done。

由索引模型根據 Issue 內容生成。