Let an entrypoint's description be edited in place (closes #392)

Each entrypoint on the webhook page has an Edit button that shows its
description as a form, with Save and Cancel, in place. Saving posts to
/hook/{id}/entrypoints/{entrypointID}/edit, behind the same login, CSRF
and ownership checks as activate, deactivate and delete, and writes only
the description column, so the URL never changes. An empty description
shows as "Entrypoint". Activate and deactivate now write only the active
column, so they cannot write back an older description over an edit.

Model: opus-5-5

internal/server/routes.go

@@ -289,6 +289,10 @@ func (s *Server) setupSourceRoutes() {
 			"/entrypoints",
 			s.h.HandleEntrypointCreate(),
 		)
+		r.Post(
+			"/entrypoints/{entrypointID}/edit",
+			s.h.HandleEntrypointEdit(),
+		)
 		r.Post(
 			"/entrypoints/{entrypointID}/delete",
 			s.h.HandleEntrypointDelete(),