Add a runnable `examples/dedicated_registrar.py` + a "A dedicated
registrar" subsection in `guide/discovery.rst` demoing the
registrar decoupled from any app tree's root: boot a bare
`tractor.run_daemon([], registry_addrs=[...])` as its own process
(a root actor that does nothing but hold the registry), point the
app tree at the same `registry_addrs`, and discover a service
*through* that external registrar.
This is the buildable-today form of the #472
"Registrar-as-subsystem (not the root actor)" bullet. Two
constraints are called out inline as follow-ups:
`enable_transports` is single-proto per runtime (no multi-backend
registrar yet), and a registrar can only be a root (no `actor_cls`
hook on `start_actor()` to spawn one as a subactor).
(this patch was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code
Gud Boi