feat: add Pub operation type, HandlerKind::Sink, call.published wire event (ADR-046)

The call protocol had Subscription (server→client streaming) but lacked
the directional complement: client→server streaming, where the initiator
produces a stream and the responder's handler consumes it. This gap was
inherited from the @alkdev/pubsub EventEnvelope prior art, which has
subscribe but no wire-level publish.

ADR-046 adds the Pub primitive:
- OperationType::Pub (client→server streaming)
- OperationType::Subscription renamed to Sub (wire: "subscription" → "sub")
- SinkHandler type + HandlerKind::Sink variant
- PublishStream type alias (Stream<Item = Result<Value, CallError>>)
- OperationRegistry::invoke_sink() dispatch path
- call.published wire event (sixth event type, additive)
- OperationSpec.publish_schema (Option<Value>, validates per-chunk input)
- DispatchResult::Sink + SinkDispatch (handler future + chunk channel)
- Dispatcher::pump_sink (feeds call.published chunks from wire to handler)
- CallConnection::publish() / publish_with_payload() client methods
- from_call sink forwarding handler (make_sink_forwarding_handler)
- make_sink_handler() helper

Fan-out/broker (one producer, N consumers, topic matching) is deferred to
the channels session — the call protocol is point-to-point; the broker is
a routing concern that sits above it. The Pub primitive is the
load-bearing piece the broker will compose on.

- 23 new tests (366 total, up from 343)
- clippy clean, fmt clean

Verification:
  cargo test                                    — 366 passed
  cargo clippy --all-targets -- -D warnings      — clean
  cargo fmt --check                              — clean

docs/architecture/README.md

@@ -98,15 +98,16 @@ are wire-stable and unchanged — see ADR-004.
 | [043](decisions/043-channelclient.md) | ChannelClient | Transport-agnostic from_connection |
 | [044](decisions/044-channels-subcrate-decomposition.md) | Channels Sub-Crate Decomposition | channels-core / channels-call (modules in alkcall) |
 | [045](decisions/045-alknetclient-native-dial-seam.md) | AlknetClient Dial Seam | spawn_dispatch / from_connection take-over; dial in consumer |
+| [046](decisions/046-publish-operation-type-and-handler-kind-sink.md) | Publish Operation Type and HandlerKind::Sink | `OperationType::Pub` (client→server streaming); `SinkHandler` + `HandlerKind::Sink`; `call.published` wire event; `invoke_sink()` dispatch; `Subscription` renamed to `Sub` |
 
 ## Relevant Open Questions
 
 See [open-questions.md](open-questions.md) for the full tracker. Key
 questions affecting this crate:
 
-- **OQ-01**: Call protocol pub/sub primitive (open) — the call protocol
-  has `subscribe` but no `pub`; needed for channels `channel/resources/
-  subscribe` fan-out. This is the next ADR to write.
+- **OQ-01**: Call protocol pub/sub primitive (partially resolved) —
+  ADR-046 adds the `Pub` primitive (client→server streaming). The
+  fan-out/broker is deferred to channels.
 - **OQ-02**: Full channel-level flow-control windowing (deferred(scope))
   — bounded-buffer is decided (ADR-040); full windowing blocked on a real
   HOL-blocking deployment observation.