Feature idea: singleton collections (collections with exactly one entry)

[dennisklappe]

Hi. Really enjoying emdash. I'd like to propose a small singleton support flag for collections.

Problem. Some collections are inherently one of a kind: a homepage, an "about" page, a global settings record. Modeling them as a normal collection means the sidebar links to a list view that always holds exactly one entry, so editing takes two clicks (the collection, then the single entry) and the UI shows "Add new" and delete affordances that don't apply.

Proposal. A "singleton" value in a collection's supports array:

• the admin sidebar item links straight to the single entry's editor (no list step);
• the content-list route redirects to that entry;
• it implies "locked" (the one entry can be edited but not created or deleted), reusing the existing locked enforcement on the create and delete handlers.

Status. I've implemented it in my fork, dennisklappe/emdash-klappe. It's a small, additive change to the support flags plus the admin sidebar and content-list route, with the create/delete guard reusing the existing locked path. Happy to open a PR if you'd want this upstream. Just let me know about the CLA and your preferred shape.

(The fork also adds nested sidebar subfolders via slash-delimited group paths, for example "Pages/Legal", if that is interesting separately.)