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/channels/session.rs

@@ -48,8 +48,8 @@
 
 use super::*;
 
-use smarm::gen_server::{self, GenServer, ServerCtx};
-use smarm::{Down, ServerRef, Watcher};
+use smarm::gen_server::{self, GenServer, GenServerCtx};
+use smarm::{Down, GenServerRef, Watcher};
 
 use std::collections::VecDeque;
 use std::hash::Hash;
@@ -87,7 +87,7 @@ pub trait ChannelSession<P>: Send + 'static {
 pub(super) struct SessionFactory<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> {
     inner: Arc<dyn ChannelFactory<P>>,
     keyfn: fn(&str, &P) -> K,
-    registry: ServerRef<Registry<P, K>>,
+    registry: GenServerRef<Registry<P, K>>,
 }
 
 /// The registry's working bounds for a session key.
@@ -140,14 +140,14 @@ pub(super) struct Join<P: Send + Sync + 'static, K> {
     inbound: Receiver<In<P>>,
 }
 
-struct Registry<P: Send + Sync + 'static, K> {
+struct Registry<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> {
     factory: Arc<dyn ChannelFactory<P>>,
     cap: usize,
     ttl: Duration,
     sessions: HashMap<K, (Pid, Sender<Ctl<P>>)>,
     /// Reverse index for `handle_down` — the reason `Key: Clone`.
     pid_key: HashMap<Pid, K>,
-    watcher: Option<Watcher>,
+    watcher: Option<Watcher<Registry<P, K>>>,
 }
 
 impl<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> GenServer for Registry<P, K> {
@@ -155,8 +155,9 @@ impl<P: Encode + Decode + Send + Sync + 'static, K: SessionKey> GenServer for Re
     type Reply = ();
     type Cast = Join<P, K>;
     type Info = ();
+    type Timer = ();
 
-    fn init(&mut self, ctx: &ServerCtx) {
+    fn init(&mut self, ctx: &GenServerCtx<Self>) {
         self.watcher = Some(ctx.watcher());
     }