port(smarm): track HEAD efbc254 — RFC 014/015 API sync

- gen_server rename (RFC 015, 3e31606): ServerRef/ServerCtx/ServerBuilder
  -> GenServerRef/GenServerCtx/GenServerBuilder across conn_actor,
  conn_registry, serve, pubsub, channels::session.
- type Timer = () on the three GenServer impls (RFC 015, 57eadb5);
  handle_timer/handle_idle/tick_every stay defaulted — opt-in later.
- Watcher and GenServerCtx are now generic over the server type: watcher
  fields typed Watcher<Table<M>> / Watcher<Registry<P, K>>; Registry's
  struct bounds strengthened to its GenServer impl bounds
  (P: Encode + Decode + Send + Sync + 'static, K: SessionKey) so the
  Watcher field's G: GenServer bound is satisfiable at the declaration.
- RFC 014 (a866e34) registry: register is (Name<M>, Sender<M>), self-only
  — a name is a typed messaging endpoint, not a pid tag. The
  introspection-only urus.server / urus.listener.{i} bindings are dropped
  rather than faked with unit channels; the whereis integration test is
  deleted; a proper messageable-name design is icebox'd in ROADMAP.md.
- Audit vs smarm 6c2b7e9 (queued messages dropped when Receiver drops):
  pubsub's prune-on-send-failure retain still holds — send Errs once
  receiver_alive is false, so a dropped rx prunes on next broadcast,
  exactly what subscriber_count's doc already promised. Freeing stranded
  Arc<M> broadcasts is strictly good. No change needed.
- The 7x E0283 in channels/mod.rs were cascade fallout of the generics
  changes; dissolved with the port, as discovery predicted.

Suite: 90 lib + 45 integration + 2 doc, green under default, smarm-trace,
phoenix, and all-features. 3 pre-existing clippy lints (conn.rs,
parser.rs, conn_actor.rs; clippy 1.97 strictness) deferred to a follow-up
chore commit to keep this diff pure.

ROADMAP.md

@@ -378,3 +378,9 @@ reconnect cycles.
 - **Bench suite** — `urus-bench-spec.md` exists in the artefact store;
   wire it up once v0.2 lands (supervision changes the hot path not at all,
   but prove it).
+- **Operator introspection via typed names** — the v0.2-era
+  `urus.server` / `urus.listener.{i}` pid tags were dropped in the
+  RFC 014 port (names are messageable endpoints now, self-registered
+  with a real `Sender<M>`). If wanted back, do it properly: register the
+  serve loop's shutdown/control channel under a typed `urus.server`
+  name instead of faking pid tags with unit channels.