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.

src/conn_registry.rs

@@ -33,7 +33,7 @@
 //! (roadmap v0.4+), which is why it exists as its own module rather than
 //! being inlined into `serve`.
 
-use smarm::{GenServer, Pid, ServerBuilder, ServerRef};
+use smarm::{GenServer, Pid, GenServerBuilder, GenServerRef};
 
 use std::collections::HashMap;
 
@@ -86,6 +86,7 @@ impl GenServer for ConnRegistry {
     type Reply = Reply;
     type Cast  = Cast;
     type Info  = ();
+    type Timer = ();
 
     fn handle_call(&mut self, request: Call) -> Reply {
         match request {
@@ -137,8 +138,8 @@ impl GenServer for ConnRegistry {
     }
 }
 
-pub fn start() -> ServerRef<ConnRegistry> {
-    ServerBuilder::new(ConnRegistry::default()).start()
+pub fn start() -> GenServerRef<ConnRegistry> {
+    GenServerBuilder::new(ConnRegistry::default()).start()
 }
 
 // ---------------------------------------------------------------------------
@@ -149,13 +150,13 @@ pub fn start() -> ServerRef<ConnRegistry> {
 /// unwind, and panic unwind alike; the cast is infallible from the
 /// guard's perspective (a dead registry just returns an ignored Err).
 pub struct DeregisterGuard {
-    registry: ServerRef<ConnRegistry>,
+    registry: GenServerRef<ConnRegistry>,
     pid:      Pid,
     make:     fn(Pid) -> Cast,
 }
 
 impl DeregisterGuard {
-    pub fn new(registry: ServerRef<ConnRegistry>, pid: Pid, make: fn(Pid) -> Cast) -> Self {
+    pub fn new(registry: GenServerRef<ConnRegistry>, pid: Pid, make: fn(Pid) -> Cast) -> Self {
         Self { registry, pid, make }
     }
 }