Port the per-user webhook endpoints (/user/settings/webhooks) from /api/v1 to
the Huma-backed /api/v2: list, available events, create, update, delete. They
are the project-less sibling of the project webhooks (#2858) and share the
webhooks.enabled gate, checked inside the registrar.
Webhook.ReadAll is extended to serve the user-level list (scoped to the
authenticated user) so the v2 list handler can go through handler.DoReadAll like
the project list; the project branch is unchanged. Credentials are masked on
read via the model's existing maskCredentials, matching #2858.
kolaente