Projects live at URLs, have owners, and are edited together live

A project is only ever at /p/<id>/<slug>; / is the index of the projects
you own or edit. Every project has an owner, who can name editors;
anyone with the link can view. Every edit saves itself, one request in
flight at a time, as a patch of the leaves that changed, and a websocket
(channels + daphne) carries presence and each committed write to
everyone else in the project. The first write to a leaf wins, and the
loser is told.

Undo is per person: a step undoes only if the leaves it touched still
hold what it left, so it never takes a collaborator's work with it.
Named snapshots replace saving, and restore as an ordinary write.

An empty symbol now survives the leaf round trip with `:nodes {}`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/urls.py

@@ -10,6 +10,10 @@ urlpatterns = [
     # ARTHUR_URL can stay pointed at the same place and only the port moves.
     path("", views.page, name="page"),
     path("index.html", views.page),
+    # A project's own address, with its name as a slug for people to read. The
+    # same page; the client reads the id out of the path and opens it.
+    path("p/<uuid:project_id>", views.page),
+    path("p/<uuid:project_id>/<slug:slug>", views.page),
     path("api/", include("clips.urls")),
     path("blob/<str:digest>", views.blob, name="blob"),
     path("admin/", admin.site.urls),