feat(call/client/from-call-streaming-forwarding): branch from_call forwarding on op_type

Subscription ops discovered via services/list + services/schema now
register a StreamingHandler (HandlerKind::Stream) that calls
CallConnection::subscribe_with_payload and forwards the remote stream
end-to-end (ADR-049 §8). Query/Mutation ops keep the existing
make_forwarding_handler (HandlerKind::Once).

- Add CallConnection::subscribe_with_payload(payload) mirroring
  call_with_payload so the forwarding handler can populate forwarded_for
  (ADR-032) + auth_token on the subscription payload. subscribe() now
  delegates to subscribe_with_payload.
- Add make_streaming_forwarding_handler() in from_call.rs using
  make_streaming_handler + futures::stream::once(...).flatten() to await
  subscribe_with_payload then forward its stream.
- Branch build_bundles on spec.op_type (already parsed by rebuild_spec_for).
- Reuse build_forwarded_payload — no new payload-construction code.
- composition_authority: None, scoped_env: None for FromCall streaming
  leaves (same as Query/Mutation FromCall leaves).
- Abort cascade (ADR-016 §6) already wired via PendingRequestMap in
  subscribe_with_payload.

Closes the gap where a from_call-imported Subscription truncated to the
first value.

crates/alknet-call/src/protocol/connection.rs

@@ -168,11 +168,26 @@ impl CallConnection {
         operation_id: &str,
         input: Value,
     ) -> impl Stream<Item = ResponseEnvelope> {
-        let request_id = generate_request_id();
         let payload = serde_json::json!({
             "operationId": operation_id,
             "input": input,
         });
+        self.subscribe_with_payload(payload).await
+    }
+
+    /// Subscribe to a remote op with a caller-constructed `call.requested`
+    /// payload. The payload MUST include `operationId` and `input`; the
+    /// caller may add `forwarded_for` (ADR-032) and `auth_token` (ADR-017 §7)
+    /// for the hub forwarding path used by `from_call`'s streaming forwarding
+    /// handler. Mirrors [`call_with_payload`](Self::call_with_payload) so the
+    /// forwarding handler can populate `forwarded_for` + `auth_token` on the
+    /// subscription payload (the plain [`subscribe`](Self::subscribe) builds
+    /// the payload internally and omits those fields).
+    pub async fn subscribe_with_payload(
+        &self,
+        payload: Value,
+    ) -> impl Stream<Item = ResponseEnvelope> {
+        let request_id = generate_request_id();
 
         let connection = match &self.connection {
             Some(c) => c,